KEYPROV Working Group A. Doherty
Internet-Draft RSA, The Security Division of EMC
Intended status: Standards Track M. Pei
Expires: March 11, 2011 VeriSign, Inc.
S. Machani
Diversinet Corp.
M. Nystrom
Microsoft Corp.
September 7, 2010
Dynamic Symmetric Key Provisioning Protocol (DSKPP)draft-ietf-keyprov-dskpp-14.txt
Abstract
DSKPP is a client-server protocol for initialization (and
configuration) of symmetric keys to locally and remotely accessible
cryptographic modules. The protocol can be run with or without
private-key capabilities in the cryptographic modules, and with or
without an established public-key infrastructure.
Two variations of the protocol support multiple usage scenarios.
With the four-pass variant, keys are mutually generated by the
provisioning server and cryptographic module; provisioned keys are
not transferred over-the-wire or over-the-air. The two-pass variant
enables secure and efficient download and installation of pre-
generated symmetric keys to a cryptographic module.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 11, 2011.
Copyright Notice
Doherty, et al. Expires March 11, 2011 [Page 1]

Internet-Draft DSKPP September 2010
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Doherty, et al. Expires March 11, 2011 [Page 2]

Internet-Draft DSKPP September 20101. Introduction
Symmetric key based cryptographic systems (e.g., those providing
authentication mechanisms such as one-time passwords and challenge-
response) offer performance and operational advantages over public
key schemes. Such use requires a mechanism for provisioning of
symmetric keys providing equivalent functionality to mechanisms such
as CMP [RFC4210] and CMC [RFC5272] in a Public Key Infrastructure.
Traditionally, cryptographic modules have been provisioned with keys
during device manufacturing, and the keys have been imported to the
cryptographic server using, e.g., a CD-ROM disc shipped with the
devices. Some vendors also have proprietary provisioning protocols,
which often have not been publicly documented (CT-KIP is one
exception [RFC4758]).
This document describes the Dynamic Symmetric Key Provisioning
Protocol (DSKPP), a client-server protocol for provisioning symmetric
keys between a cryptographic module (corresponding to DSKPP client)
and a key provisioning server (corresponding to DSKPP server).
DSKPP provides an open and interoperable mechanism for initializing
and configuring symmetric keys to cryptographic modules that are
accessible over the Internet. The description is based on the
information contained in [RFC4758], and contains specific
enhancements, such as User Authentication and support for the [PSKC]
format for transmission of keying material.
DSKPP has two principal protocol variants. The four-pass protocol
variant permits a symmetric key to be established that includes
randomness contributed by both the client and the server. The two-
pass protocol requires only one round trip instead of two and permits
a server specified key to be established.
1.1. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
1.2. Version Support
There is a provision made in the syntax for an explicit version
number. Only version "1.0" is currently specified.
The purpose for versioning the protocol is to provide a mechanism by
which changes to required cryptographic algorithms (e.g., SHA-256)
and attributes (e.g., key size) can be deployed without disrupting
Doherty, et al. Expires March 11, 2011 [Page 6]

Internet-Draft DSKPP September 2010
existing implementations; likewise, out-dated implementations can be
de-commissioned without disrupting operations involving newer
protocol versions.
The numbering scheme for DSKPP versions is "<major>.<minor>". The
major and minor numbers MUST be treated as separate integers and each
number MAY be incremented higher than a single digit. Thus, "DSKPP
2.4" would be a lower version than "DSKPP 2.13", which in turn would
be lower than "DSKPP 12.3". Leading zeros (e.g., "DSKPP 6.01") MUST
be ignored by recipients and MUST NOT be sent.
The major version number should be incremented only if the data
formats or security algorithms have changed so dramatically that an
older version implementation would not be able to interoperate with a
newer version (e.g., removing support for a previously mandatory-to-
implement algorithm now found to be insecure). The minor version
number indicates new capabilities (e.g., introducing a new algorithm
option) and MUST be ignored by an entity with a smaller minor version
number, but used for informational purposes by the entity with the
larger minor version number.
1.3. Namespace Identifiers
This document uses Uniform Resource Identifiers [RFC3986] to identify
resources, algorithms, and semantics.
1.3.1. Defined Identifiers
The XML namespace [XMLNS] URI for Version 1.0 of DSKPP protocol is:
"urn:ietf:params:xml:ns:keyprov:dskpp"
References to qualified elements in the DSKPP schema defined herein
use the prefix "dskpp", but any prefix is allowed.
1.3.2. Identifiers Defined in Related Specifications
This document relies on qualified elements already defined in the
Portable Symmetric Key Container [PSKC] namespace, which is
represented by the prefix "pskc" and declared as:
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:pskc"
1.3.3. Referenced Identifiers
Finally, the DSKPP syntax presented in this document relies on
algorithm identifiers defined in the XML Signature [XMLDSIG]
namespace:
Doherty, et al. Expires March 11, 2011 [Page 7]

Internet-Draft DSKPP September 2010
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
References to algorithm identifiers in the XML Signature namespace
are represented by the prefix "ds".
2. Terminology2.1. Definitions
The definitions provided below are defined as used in this document.
The same terms may be defined differently in other documents.
Authentication Code (AC): User Authentication Code comprised of a
string of hexadecimal characters known to the device and the
server and containing at a minimum a client identifier and a
password. This ClientID/password combination is used only once
and may have a time limit, and then discarded.
Authentication Data (AD): User Authentication Data that is derived
from the Authentication Code (AC)
Client ID: An identifier that the DSKPP Server uses to locate the
real user name or account identifier on the server. It can be a
short random identifier that is unrelated to any real usernames.
Cryptographic Module: A component of an application, which enables
symmetric key cryptographic functionality
Device: A physical piece of hardware, or a software framework, that
hosts symmetric key cryptographic modules
Device ID (DeviceID): A unique identifier for the device that houses
the cryptographic module, e.g., a mobile phone
DSKPP Client: Manages communication between the symmetric key
cryptographic module and the DSKPP server
DSKPP Server: The symmetric key provisioning server that
participates in the DSKPP protocol run
DSKPP Server ID (ServerID): The unique identifier of a DSKPP server
Key Agreement: A key establishment protocol whereby two or more
parties can agree on a key in such a way that both influence the
outcome
Doherty, et al. Expires March 11, 2011 [Page 8]

Internet-Draft DSKPP September 2010
Key Confirmation: The assurance of the rightful participants in a
key-establishment protocol that the intended recipient of the
shared key actually possesses the shared key
Key Issuer: An organization that issues symmetric keys to end-users
Key Package (KP): An object that encapsulates a symmetric key and
its configuration data
Key ID (KeyID): A unique identifier for the symmetric key
Key Protection Method (KPM): The key transport method used during
two-pass DSKPP
Key Protection Method List (KPML): The list of key protection
methods supported by a cryptographic module
Key Provisioning Server: A lifecycle management system that provides
a key issuer with the ability to provision keys to cryptographic
modules hosted on end-users' devices
Key Transport: A key establishment procedure whereby the DSKPP
server selects and encrypts the keying material and then sends
the material to the DSKPP client [NIST-SP800-57]
Key Transport Key: The private key that resides on the cryptographic
module. This key is paired with the DSKPP client's public key,
which the DSKPP server uses to encrypt keying material during key
transport [NIST-SP800-57]
Key Type: The type of symmetric key cryptographic methods for which
the key will be used (e.g., OATH HOTP or RSA SecurID
authentication, AES encryption, etc.)
Key Wrapping: A method of encrypting keys for key transport
[NIST-SP800-57]
Key Wrapping Key: A symmetric key encrypting key used for key
wrapping [NIST-SP800-57]
Keying Material: The data necessary (e.g., keys and key
configuration data) necessary to establish and maintain
cryptographic keying relationships [NIST-SP800-57]
Doherty, et al. Expires March 11, 2011 [Page 9]

Internet-Draft DSKPP September 2010
Manufacturer's Key A unique master key pre-issued to a hardware
device, e.g., a smart card, during the manufacturing process. If
present, this key may be used by a cryptographic module to derive
secret keys
Protocol Run: Complete execution of the DSKPP that involves one
exchange (2-pass) or two exchanges (4-pass)
Security Attribute List (SAL): A payload that contains the DSKPP
version, DSKPP variant (four- or two-pass), key package formats,
key types, and cryptographic algorithms that the cryptographic
module is capable of supporting
2.2. Notation
|| String concatenation
[x] Optional element x
A ^ B Exclusive-OR operation on strings A and B (where
A and B are of equal length)
<XMLElement> A typographical convention used in the body of
the text
DSKPP-PRF(k,s,dsLen) A keyed pseudo-random function
E(k,m) Encryption of m with the key k
K Key used to encrypt R_C (either K_SERVER or
K_SHARED), or in MAC or DSKPP_PRF computations
K_AC Secret key that is derived from the
Authentication Code and used for user
authentication purposes
K_MAC Secret key derived during a DSKPP exchange for
use with key confirmation
K_MAC' A second secret key used for server
authentication
K_PROV A provisioning master key from which two keys are
derived: K_TOKEN and K_MAC
K_SERVER Public key of the DSKPP server; used for
encrypting R_C in the four-pass protocol variant
K_SHARED Secret key that is pre-shared between the DSKPP
client and the DSKPP server; used for encrypting
R_C in the four-pass protocol variant
K_TOKEN Secret key that is established in a cryptographic
module using DSKPP
R Pseudorandom value chosen by the DSKPP client and
used for MAC computations
Doherty, et al. Expires March 11, 2011 [Page 10]

Internet-Draft DSKPP September 2010
Client: The DSKPP client which manages communication between the
cryptographic module and the key provisioning server.
The principal syntax is XML [XML] and it is layered on a transport
mechanism such as HTTP [RFC2616] and HTTP Over TLS [RFC2818]. While
it is highly desirable for the entire communication between the DSKPP
client and server to be protected by means of a transport providing
confidentiality and integrity protection such as HTTP over Transport
Layer Security (TLS), such protection is not sufficient to protect
the exchange of the symmetric key data between the server and the
cryptographic module and the DSKPP protocol is designed to permit
implementations that satisfy this requirement.
The server only communicates to the client. As far as the server is
concerned, the client and cryptographic module may be considered to
be a single entity.
From a client-side security perspective, however, the client and the
cryptographic module are separate logical entities and may in some
implementations be separate physical entities as well.
It is assumed that a device will host an application layered above
the cryptographic module, and this application will manage
communication between the DSKPP client and cryptographic module. The
manner in which the communicating application will transfer DSKPP
protocol elements to and from the cryptographic module is transparent
to the DSKPP server. One method for this transfer is described in
[CT-KIP-P11].
3.2. Basic DSKPP Exchange3.2.1. User Authentication
In a DSKPP message flow, the user has obtained a new hardware or
software device embedded with a cryptographic module. The goal of
DSKPP is to provision the same symmetric key and related information
to the cryptographic module and the key management server, and
associate the key with the correct user name (or other account
identifier) on the server. To do this, the DSKPP Server MUST
authenticate the user to be sure he is authorized for the new key.
User authentication occurs within the protocol itself after__ the
DSKPP client initiates the first message. In this case, the DSKPP
client MUST have access to the DSKPP Server URL.
Alternatively, a DSKPP web service or other form of web application
can authenticate a user before__ the first message is exchanged. In
this case, the DSKPP server MUST trigger the DSKPP client to initiate
Doherty, et al. Expires March 11, 2011 [Page 12]

Internet-Draft DSKPP September 2010
o The user typically enters the Client ID and Authentication Code
manually, possibly on a device with only numeric keypad. Thus,
they are often short numeric values (for example, 8 decimal
digits). However, the DSKPP Server is free to generate them in
any way it wishes.
o The DSKPP client needs the URL [RFC3986] of the DSKPP server
(which is not user-specific or secret, and may be pre-configured
somehow), and a set of trust anchors for verifying the server
certificate.
o There must be an account for the user that has an identifier and
long-term user name (or other account identifier) to which the
token will be associated. The DSKPP server will use the Client ID
to find the corresponding Authentication Code for user
authentication.
In Step 1, the client establishes a TLS connection, and authenticates
the server (that is, validates the certificate, and compares the host
name in the URL with the certificate) as described in Section 3.1 of
[RFC2818].
Next, the DSKPP Client and DSKPP Server exchange DSKPP messages
(which are sent over HTTPS). In these messages:
o The client and server negotiate which cryptographic algorithms
they want to use; which algorithms are supported for protecting
DSKPP messages, and other DSKPP protocol details.
o The client sends the Client ID to the server, and proves that it
knows the corresponding Authentication Code.
o The client and server agree on a secret key (token key or
K_TOKEN); depending on the negotiated protocol variant, this is
either a fresh key derived during the DSKPP protocol run (called
"four-pass variant", since it involves four DSKPP messages), or it
is generated by (or pre-exists on) the server and transported to
the client (called "two-pass variant" in the rest of this
document, since it involves two DSKPP messages).
o The server sends a "key package" to the client. The package only
includes the key itself in the case of the "two-pass variant";
with either variant, the key package contains attributes that
influence how the provisioned key will be later used by the
cryptographic module and cryptographic server. The exact contents
depend on the cryptographic algorithm (e.g., for a one-time
password algorithm that supports variable-length OTP values, the
length of the OTP value would be one attribute in the key
package).
After the protocol run has been successfully completed, the
cryptographic modules stores the contents of the key package.
Likewise, the DSKPP provisioning server stores the contents of the
key package with the cryptographic server, and associates these with
Doherty, et al. Expires March 11, 2011 [Page 14]

Internet-Draft DSKPP September 2010
the correct user name. The user can now use the their device to
perform symmetric-key based operations.
The exact division of work between the cryptographic module and the
DSKPP client -- and key Provisioning server and DSKPP server -- are
not specified in this document. The figure above shows one possible
case, but this is intended for illustrative purposes only.
3.2.3. Protocol Triggered by the DSKPP Server
In the first message flow (previous section), the Client ID and
Authentication Code were delivered to the client by some out-of-band
means (such as paper sent to the user).
Web DSKPP DSKPP Web
Browser Client Server Server
| | | |
|<-------- HTTPS browsing + some kind of user auth. --------->|
| | | |
| some HTTP request ----------------------------------------->|
| | |
| | |<------------->|
| | | |
|<----------------------- HTTP response with <KeyProvTrigger> |
| | | |
| Trigger ---->| | |
| | | |
| |<-- 1. TLS handshake with --->| |
| | server auth. | |
| | | |
| | ... continues... | |
Figure 2: DSKPP Exchange with Web-Based Authentication
In the second message flow, the user first authenticates to a web
server (for example, IT department's "self-service" Intranet page),
using an ordinary web browser and some existing credentials.
The user then requests (by clicking a link or submitting a form)
provisioning of a new key to the cryptographic module. The web
server will reply with a <KeyProvTrigger> message that contains the
Client ID, Authentication Code, and URL of the DSKPP server. This
information is also needed by the DSKPP server; how the web server
and DSKPP server interact is beyond the scope of this document.
The <KeyProvTrigger> message is sent in a HTTP response, and it is
marked with MIME type "application/dskpp+xml". It is assumed the web
browser has been configured to recognize this MIME type; the browser
Doherty, et al. Expires March 11, 2011 [Page 15]

Internet-Draft DSKPP September 2010
will start the DSKPP client, and provides it with the
<KeyProvTrigger> message.
The DSKPP client then contacts the DSKPP server, and uses the Client
ID and Authentication Code (from the <KeyProvTrigger> message) the
same way as in the first message flow.
3.2.4. Variants
As noted in the previous section, once the protocol has started, the
client and server MAY engage in either a two-pass or four-pass
message exchange. The four-pass and two-pass protocols are
appropriate in different deployment scenarios. The biggest
differentiator between the two is that the two-pass protocol supports
transport of an existing key to a cryptographic module, while the
four-pass involves key generation on-the-fly via key agreement. In
either case, both protocol variants support algorithm agility through
negotiation of encryption mechanisms and key types at the beginning
of each protocol run.
3.2.4.1. Criteria for Using the Four-Pass Variant
The four-pass protocol is needed under one or more of the following
conditions:
o Policy requires that both parties engaged in the protocol jointly
contribute entropy to the key. Enforcing this policy mitigates
the risk of exposing a key during the provisioning process as the
key is generated through mutual agreement without being
transferred over-the-air or over-the-wire. It also mitigates risk
of exposure after the key is provisioned, as the key will not be
vulnerable to a single point of attack in the system.
o A cryptographic module does not have private-key capabilities.
o The cryptographic module is hosted by a device that was neither
pre-issued with a manufacturer's key or other form of pre-shared
key (as might be the case with a smart card or SIM card) nor has a
keypad that can be used for entering a passphrase (such as present
on a mobile phone).
3.2.4.2. Criteria for Using the Two-Pass Variant
The two-pass protocol is needed under one or more of the following
conditions:
o Pre-existing (i.e., legacy) keys must be provisioned via transport
to the cryptographic module.
o The cryptographic module is hosted on a device that was pre-issued
with a manufacturer's key (such as may exist on a smart card), or
other form of pre-shared key (such as may exist on a SIM-card),
and is capable of performing private-key operations.
Doherty, et al. Expires March 11, 2011 [Page 16]

Internet-Draft DSKPP September 2010
o The cryptographic module is hosted by a device that has a built-in
keypad with which a user may enter a passphrase, useful for
deriving a key wrapping key for distribution of keying material.
3.3. Status Codes
Upon transmission or receipt of a message for which the Status
attribute's value is not "Success" or "Continue", the default
behavior, unless explicitly stated otherwise below, is that both the
DSKPP server and the DSKPP client MUST immediately terminate the
DSKPP protocol run. DSKPP servers and DSKPP clients MUST delete any
secret values generated as a result of failed runs of the DSKPP
protocol. Session identifiers MAY be retained from successful or
failed protocol runs for replay detection purposes, but such retained
identifiers MUST NOT be reused for subsequent runs of the protocol.
When possible, the DSKPP client SHOULD present an appropriate error
message to the user.
These status codes are valid in all DSKPP Response messages unless
explicitly stated otherwise:
Continue: The DSKPP server is ready for a subsequent request from
the DSKPP client. It cannot be sent in the server's final
message
Success: Successful completion of the DSKPP session. It can only be
sent in the server's final message
Abort: The DSKPP server rejected the DSKPP client's request for
unspecified reasons
AccessDenied: The DSKPP client is not authorized to contact this
DSKPP server
MalformedRequest: The DSKPP server failed to parse the DSKPP
client's request
UnknownRequest: The DSKPP client made a request that is unknown to
the DSKPP server
UnknownCriticalExtension: A DSKPP extension marked as "Critical"
could not be interpreted by the receiving party.
Doherty, et al. Expires March 11, 2011 [Page 17]

Internet-Draft DSKPP September 2010
UnsupportedVersion: The DSKPP client used a DSKPP protocol version
not supported by the DSKPP server. This error is only valid in
the DSKPP server's first response message
NoSupportedKeyTypes: "NoSupportedKeyTypes" indicates that the DSKPP
client only suggested key types that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message
NoSupportedEncryptionAlgorithms: The DSKPP client only suggested
encryption algorithms that are not supported by the DSKPP server.
This error is only valid in the DSKPP server's first response
message
NoSupportedMacAlgorithms: The DSKPP client only suggested MAC
algorithms that are not supported by the DSKPP server. This
error is only valid in the DSKPP server's first response message
NoProtocolVariants: The DSKPP client did not suggest a required
protocol variant (either 2-pass or 4-pass). This error is only
valid in the DSKPP server's first response message.
NoSupportedKeyPackages: The DSKPP client only suggested key package
formats that are not supported by the DSKPP server. This error
is only valid in the DSKPP server's first response message
AuthenticationDataMissing: The DSKPP client didn't provide
authentication data that the DSKPP server required
AuthenticationDataInvalid: The DSKPP client supplied user
authentication data that the DSKPP server failed to validate
InitializationFailed: The DSKPP server could not generate a valid
key given the provided data. When this status code is received,
the DSKPP client SHOULD try to restart DSKPP, as it is possible
that a new run will succeed
ProvisioningPeriodExpired: The provisioning period set by the DSKPP
server has expired. When the status code is received, the DSKPP
client SHOULD report the reason for key initialization failure to
the user and the user MUST register with the DSKPP server to
initialize a new key
3.4. Basic Constructs
The following calculations are used in both DSKPP protocol variants.
Doherty, et al. Expires March 11, 2011 [Page 18]

Internet-Draft DSKPP September 20103.4.1. User Authentication Data, AD
User authentication data (AD) is derived from a Client ID and
Authentication Code that the user enters before the first DSKPP
message is sent.
Note: The user will typically enter the Client ID and Authentication
Code manually, possibly on a device with only numeric keypad. Thus,
they are often short numeric values (for example, 8 decimal digits).
However, the DSKPP Server is free to generate them in any way it
wishes.
3.4.1.1. Authentication Code Format
AC is encoded in Type-Length-Value (TLV) format. The format consists
of a minimum of two TLVs and a variable number of additional TLVs,
depending on implementation.
The TLV fields are defined as follows:
Type (1 character) A hexadecimal character identifying the
type of information contained in the Value
field.
Length (2 characters) Two hexadecimal characters indicating the
length of the Value field to follow. The
field value MAY be up to 255 characters.
The Length value 00 MAY be used to specify
custom tags without any field values.
Value (variable length) A variable-length string of hexadecimal
characters containing the instance-specific
information for this TLV.
The following table summarizes the TLVs defined in this document.
Optional TLVs are allowed for vendor-specific extensions with the
constraint that the high bit MUST be set to indicate a vendor-
specific type. Other TLVs are left for later revisions of this
protocol.
Doherty, et al. Expires March 11, 2011 [Page 19]

Internet-Draft DSKPP September 2010
+------+------------+-------------------------------------------+
| Type | TLV Name | Conformance | Example Usage |
+------+------------+-------------------------------------------+
| 1 | Client ID | Mandatory | { "AC00000A" } |
+------+------------+-------------+-----------------------------+
| 2 | Password | Mandatory | { "3582AF0C3E" } |
+------+------------+-------------+-----------------------------+
| 3 | Checksum | Optional | { "4D5" } |
+------+------------+-------------+-----------------------------+
The Client ID is a mandatory TLV that represents the requester's
identifier of maximum length 255. The value is represented as a
string of hexadecimal characters that identifies the key request.
For example, suppose Client ID is set to "AC00000A", the Client ID
TLV in the AC will be represented as "108AC00000A".
The Password is a mandatory TLV the contains a one-time use shared
secret known by the user and the Provisioning Server. The password
value is unique and SHOULD be a random string to make AC more
difficult to guess. The string MUST contain hexadecimal characters
only. For example, suppose password is set to "3582AF0C3E", then the
Password TLV would be "20A3582AF0C3E".
The Checksum is an OPTIONAL TLV, which is generated by the issuing
server and sent to the user as part of the AC. If the TLV is
provided, the checksum value MUST be computed using the CRC16
algorithm [ISO3309]. When the user enters the AC, the typed AC
string of characters is verified with the checksum to ensure it is
correctly entered by the user. For example, suppose the AC with
combined Client ID tag and Password tag is set to
"108AC00000A20A3582AF0C3E", then the CRC16 calculation would generate
a checksum of 0x356, resulting in a Checksum TLV of "334D5". The
complete AC string in this example would be
"108AC00000A20A3582AF0C3E3034D5".
Although this specification recommends using hexadecimal characters
only for the AC at the application's user interface layer and making
the TLV triples non-transparent to the user as described in the
example above; implementations MAY additionally choose to use other
printable Unicode characters [UNICODE] at the application's user
interface layer in order to meet specific local, context or usability
requirements. When non-hexadecimal characters are desired at the
user interface layer such as when other printable US-ASCII characters
or international characters are used, SASLprep [RFC4013] MUST be used
to normalize user input before converting it to a string of
hexadecimal characters. For example, if a given application allows
use of any printable US-ASCII characters and extended ASCII
characters for Client ID and password fields and the Client ID is set
Doherty, et al. Expires March 11, 2011 [Page 20]

Internet-Draft DSKPP September 2010
to "myclient!D" and associated password is set to "mYpas&#rD", the
user enters through the keyboard or other means a Client ID of
"myclient!D" and a password of "mYpas&#rD" in separate form fields or
as instructed by the provider. The application's layer processing
user input MUST then convert the values entered by the user to the
following string for use in the protocol:
"1146D79636C69656E7421442126D5970617326237244" (note that in this
example the Checksum TLV is not added).
The example is explained further below in detail:
Assume that the raw Client ID value or the value entered by the use
is: myclient!ID
The Client ID value as characters names is:
U+006D LATIN SMALL LETTER M character
U+0079 LATIN SMALL LETTER Y character
U+0063 LATIN SMALL LETTER C character
U+006C LATIN SMALL LETTER L character
U+0069 LATIN SMALL LETTER I character
U+0065 LATIN SMALL LETTER E character
U+006E LATIN SMALL LETTER N character
U+0074 LATIN SMALL LETTER T character
U+0021 EXCLAMATION MARK character (!)
U+0044 LATIN CAPITAL LETTER D character
The UTF-8 conversion of the Client ID value is: 6D 79 63 6C 69 65 6E
74 21 44
The length of the Client ID value in hexadecimal characters is: 14
The TLV presentation of the Client ID field is:
1146D79636C69656E742144
The raw password value or the value entered by the user is: mYpas&#rD
The password value as character names is:
U+006D LATIN SMALL LETTER M character
U+0059 LATIN LARGE LETTER Y character
U+0070 LATIN SMALL LETTER P character
U+0061 LATIN SMALL LETTER A character
U+0073 LATIN SMALL LETTER S character
U+0026 AMPERSAND character (&)
U+0023 POUND SIGN character (#)
Doherty, et al. Expires March 11, 2011 [Page 21]

Internet-Draft DSKPP September 2010
U+0072 LATIN SMALL LETTER R character
U+0044 LATIN LARGE LETTER D character
The UTF-8 conversion of the password value is: 6D 59 70 61 73 26 23
72 44
The length of the password value in hexadecimal characters is: 12
The TLV presentation of the password field is: 2126D5970617326237244
The combined Client ID and password fields value or the AC value is:
1146D79636C69656E7421442126D5970617326237244
3.4.1.2. User Authentication Data Calculation
The Authentication Data consists of a Client ID (extracted from the
AC) and a value, which is derived from AC as follows (refer to
Section 3.4.2 for a description of DSKPP-PRF in general and
Appendix D for a description of DSKPP-PRF-AES):
MAC = DSKPP-PRF(K_AC, AC->ClientID||URL_S||R_C||[R_S], 16)
In four-pass DSKPP, the cryptographic module uses R_C, R_S, and URL_S
to calculate the MAC, where URL_S is the URL the DSKPP client uses
when contacting the DSKPP server. In two-pass DSKPP, the
cryptographic module does not have access to R_S, therefore only R_C
is used in combination with URL_S to produce the MAC. In either
case, K_AC MUST be derived from AC->password as follows [PKCS-5]:
K_AC = PBKDF2(AC->password, R_C || K, iter_count, 16)
One of the following values for K MUST be used:
a. In four-pass:
* The public key of the DSKPP server (K_SERVER), or (in the pre-
shared key variant) the pre-shared key between the client and
the server (K_SHARED)
b. In two-pass:
* The public key of the DSKPP client, or the public key of the
device when a device certificate is available
* The pre-shared key between the client and the server
(K_SHARED)
* A passphrase-derived key
The iteration count, iter_count, MUST be set to at least 100,000
except in the last two two-pass cases (where K is set to K_SHARED or
a passphrase-derived key), in which case iter_count MUST be set to 1.
Doherty, et al. Expires March 11, 2011 [Page 22]

Internet-Draft DSKPP September 20103.4.2. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF
Regardless of the protocol variant employed, there is a requirement
for a cryptographic primitive that provides a deterministic
transformation of a secret key k and a varying length octet string s
to a bit string of specified length dsLen.
This primitive must meet the same requirements as for a keyed hash
function: It MUST take an arbitrary length input, and generate an
output that is one-way and collision-free (for a definition of these
terms, see, e.g., [FAQ]). Further, its output MUST be unpredictable
even if other outputs for the same key are known.
From the point of view of this specification, DSKPP-PRF is a "black-
box" function that, given the inputs, generates a pseudorandom value
and MAY be realized by any appropriate and competent cryptographic
technique. Appendix D contains two example realizations of DSKPP-
PRF.
DSKPP-PRF(k, s, dsLen)
Input:
k secret key in octet string format
s octet string of varying length consisting of variable data
distinguishing the particular string being derived
dsLen desired length of the output
Output:
DS pseudorandom string, dsLen-octets long
For the purposes of this document, the secret key k MUST be at least
16 octets long.
3.4.3. The DSKPP Message Hash Algorithm
When sending its last message in a protocol run, the DSKPP server
generates a MAC that is used by the client for key confirmation.
Computation of the MAC MUST include a hash of all DSKPP messages sent
by the client and server during the transaction. To compute a
message hash for the MAC given a sequence of DSKPP messages msg_1,
..., msg_n, the following operations MUST be carried out:
Doherty, et al. Expires March 11, 2011 [Page 23]

Internet-Draft DSKPP September 2010
a. The sequence of messages contains all DSKPP Request and Response
messages up to but not including this message.
b. Re-transmitted messages are removed from the sequence of
messages.
Note: The resulting sequence of messages MUST be an alternating
sequence of DSKPP Request and DSKPP Response messages
c. The contents of each message is concatenated together.
d. The resultant string is hashed using SHA-256 in accordance with
[FIPS180-SHA].
4. Four-Pass Protocol Usage
This section describes the methods and message flow that comprise the
four-pass protocol variant. Four-pass DSKPP depends on a client-
server key agreement mechanism.
4.1. The Key Agreement Mechanism
With 4-pass DSKPP, the symmetric key that is the target of
provisioning, is generated on-the-fly without being transferred
between the DSKPP client and DSKPP server. The data flow and
computation are described below.
4.1.1. Data Flow
A sample data flow showing key generation during the 4-pass protocol
is shown in Figure 3.
Doherty, et al. Expires March 11, 2011 [Page 24]

Internet-Draft DSKPP September 2010
user. In that case, the latter string, R_C2, SHOULD be unique for
each cryptographic module.
A man-in-the-middle (in the form of corrupt client software or a
mistakenly contacted server) may present his own public key to the
cryptographic module. This will enable the attacker to learn the
client's version of K_TOKEN. However, the attacker is not able to
persuade the legitimate server to derive the same value for K_TOKEN,
since K_TOKEN is a function of the public key involved, and the
attacker's public key must be different than the correct server's (or
else the attacker would not be able to decrypt the information
received from the client). Therefore, once the attacker is no longer
"in the middle," the client and server will detect that they are "out
of sync" when they try to use their keys. In the case of encrypting
R_C with K_SERVER, it is therefore important to verify that K_SERVER
really is the legitimate server's key. One way to do this is to
independently validate a newly generated K_TOKEN against some
validation service at the server (e.g., using a connection
independent from the one used for the key generation).
4.1.2. Computation
In 4-pass DSKPP, the client and server both generate K_TOKEN and
K_MAC by deriving them from a provisioning key (K_PROV) using the
DSKPP-PRF function (refer to Section 3.4.2) as follows:
K_PROV = DSKPP-PRF(k,s,dsLen), where
k = R_C (i.e., the secret random value chosen by the DSKPP
client)
s = "Key generation" || K || R_S (where K is the key used to
encrypt R_C and R_S is the random value chosen by the DSKPP
server)
dsLen = (desired length of K_PROV whose first half constitutes
K_MAC and second half constitutes K_TOKEN)
Then K_TOKEN and K_MAC are derived from K_PROV, where
K_PROV = K_MAC || K_TOKEN
When computing K_PROV, the derived keys, K_MAC and K_TOKEN, MAY be
subject to an algorithm-dependent transform before being adopted as a
key of the selected type. One example of this is the need for parity
in DES keys.
Note that this computation pertains to 4-pass DSKPP only.
Doherty, et al. Expires March 11, 2011 [Page 26]

Internet-Draft DSKPP September 20104.2. Message Flow
The four-pass protocol flow consists of two message exchanges:
1: Pass 1 = <KeyProvClientHello>, Pass 2 = <KeyProvServerHello>
2: Pass 3 = <KeyProvClientNonce>, Pass 4 = <KeyProvServerFinished>
The first pair of messages negotiate cryptographic algorithms and
exchange nonces. The second pair of messages establishes a symmetric
key using mutually authenticated key agreement.
The purpose and content of each message are described below. XML
format and examples are in Section 8 and Appendix B.
4.2.1. KeyProvTrigger
DSKPP Client DSKPP Server
------------ ------------
[<---] AD, [DeviceID],
[KeyID], [URL_S]
When this message is sent:
The "trigger" message is optional. The DSKPP server sends this
message after the following out-of-band steps are performed:
1. A user directed their browser to a key provisioning web
application and signs in (i.e., authenticates)
2. The user requests a key
3. The web application processes the request and returns an
authentication code to the user, e.g., in response to an
enrollment request via a secure web session
4. The web application retrieves the authentication code from the
user (possibly by asking the user to enter it using a web
form, or alternatively by the user selecting a URL in which
the authentication code is embedded)
5. The web application derives authentication data (AD) from the
authentication code as described in Section 3.4.1
6. The web application passes AD, and possibly a DeviceID
(identifies a particular device to which the key is to be
provisioned) and/or KeyID (identifies a key that will be
replaced) to the DSKPP server
Purpose of this message:
To start a DSKPP session: The DSKPP server uses this message to
trigger a client-side application to send the first DSKPP message.
To provide a way for the key provisioning system to get the DSKPP
server URL to the DSKPP client.
So the key provisioning system can point the DSKPP client to a
Doherty, et al. Expires March 11, 2011 [Page 27]

Internet-Draft DSKPP September 2010
particular cryptographic module that was pre-configured in the
DSKPP provisioning server.
In the case of key renewal, to identify the key to be replaced.
What is contained in this message:
AD MUST be provided to allow the DSKPP server to authenticate the
user before completing the protocol run.
A DeviceID MAY be included to allow a key provisioning application
to bind the provisioned key to a specific device.
A KeyID MAY be included to allow the key provisioning application
to identify a key to be replaced, e.g., in the case of key
renewal.
The Server URL MAY be included to allow the key provisioning
application to inform the DSKPP client of which server to contact
4.2.2. KeyProvClientHello
DSKPP Client DSKPP Server
------------ ------------
SAL, [AD],
[DeviceID], [KeyID] --->
When this message is sent:
When a DSKPP client first connects to a DSKPP server, it is
required to send the <KeyProvClientHello> as its first message.
The client can also send a <KeyProvClientHello> in response to a
<KeyProvTrigger>.
What is contained in this message:
The Security Attribute List (SAL) included with
<KeyProvClientHello> contains the combinations of DSKPP versions,
variants, key package formats, key types, and cryptographic
algorithms that the DSKPP client supports in order of the client's
preference (favorite choice first).
If <KeyProvClientHello> was preceded by a <KeyProvTrigger>, then
this message MUST also include the Authentication (AD), DeviceID,
and/or KeyID that was provided with the trigger.
If <KeyProvClientHello> was not preceded by a <KeyProvTrigger>,
then this message MAY contain a device ID that was pre-shared with
the DSKPP server, and a key ID associated with a key previously
provisioned by the DSKPP provisioning server.
Doherty, et al. Expires March 11, 2011 [Page 28]

Internet-Draft DSKPP September 2010
Application note:
If this message is preceded by trigger message <KeyProvTrigger>,
then the application will already have AD available (see
Section 4.2.1). However, if this message was not preceded by
<KeyProvTrigger>, then the application MUST retrieve the user
authentication code, possibly by prompting the user to manually
enter their authentication code, e.g., on a device with only a
numeric keypad.
The application MUST also derive Authentication Data (AD) from the
authentication code, as described in Section 3.4.1, and save it
for use in its next message, <KeyProvClientNonce>.
How the DSKPP server uses this message:
The DSKPP server will look for an acceptable combination of DSKPP
version, variant (in this case, four-pass), key package format,
key type, and cryptographic algorithms. If the DSKPP Client's SAL
does not match the capabilities of the DSKPP Server, or does not
comply with key provisioning policy, then the DSKPP Server will
set the Status attribute to something other than "Continue".
Otherwise, Status will be set to "Continue".
If included in <KeyProvClientHello>, the DSKPP server will
validate the Authentication Data (AD), DeviceID, and KeyID. The
DSKPP server MUST NOT accept the DeviceID unless the server sent
the DeviceID in a preceding trigger message. Note that it is also
legitimate for a DSKPP client to initiate the DSKPP protocol run
without having received a <KeyProvTrigger> message from a server,
but in this case any provided DeviceID MUST NOT be accepted by the
DSKPP server unless the server has access to a unique key for the
identified device and that key will be used in the protocol.
4.2.3. KeyProvServerHello
DSKPP Client DSKPP Server
------------ ------------
<--- SAL, R_S, [K], [MAC]
When this message is sent:
The DSKPP server will send this message in response to a
<KeyProvClientHello> message after it looks for an acceptable
combination of DSKPP version, variant (in this case, four-pass),
key package format, key type, and set of cryptographic algorithms.
If it could not find an acceptable combination, then it will still
send the message, but with a failure status.
Purpose of this message:
Doherty, et al. Expires March 11, 2011 [Page 29]

Internet-Draft DSKPP September 2010
With this message, the context for the protocol run is set.
Furthermore, the DSKPP server uses this message to transmit a
random nonce, which is required for each side to agree upon the
same symmetric key (K_TOKEN).
What is contained in this message:
A status attribute equivalent to the server's return code to
<KeyProvClientHello>. If the server found an acceptable set of
attributes from the client's SAL, then it sets status to Continue
and returns an SAL (selected from the SAL that it received in
<KeyProvClientHello>). The Server's SAL specifies the DSKPP
version and variant (in this case, four-pass), key type,
cryptographic algorithms, and key package format that the DSKPP
Client MUST use for the remainder of the protocol run.
A random nonce (R_S) for use in generating a symmetric key through
key agreement; the length of R_S may depend on the selected key
type.
A key (K) for the DSKPP Client to use for encrypting the client
nonce included with <KeyProvClientNonce>. K represents the
server's public key (K_SERVER) or a pre-shared secret key
(K_SHARED).
A MAC MUST be present if a key is being renewed so that the DSKPP
client can confirm that the replacement key came from a trusted
server. This MAC MUST be computed using DSKPP-PRF (see
Section 3.4.2), where the input parameter k MUST be set to the
existing MAC key K_MAC' (i.e., the value of the MAC key that
existed before this protocol run; the implementation MAY specify
K_MAC' to be the value of the K_TOKEN that is being replaced), and
input parameter dsLen MUST be set to the length of R_S.
How the DSKPP client uses this message:
When the Status attribute is not set to "Continue", this indicates
failure and the DSKPP client MUST abort the protocol.
If successful execution of the protocol will result in the
replacement of an existing key with a newly generated one, the
DSKPP client MUST verify the MAC provided in <KeyProvServerHello>.
The DSKPP client MUST terminate the DSKPP session if the MAC does
not verify, and MUST delete any nonces, keys, and/or secrets
associated with the failed run.
If Status is set to "Continue" the cryptographic module generates
a random nonce (R_C) using the cryptographic algorithm specified
in the SAL. The length of the nonce R_C will depend on the
selected key type.
Doherty, et al. Expires March 11, 2011 [Page 30]

Internet-Draft DSKPP September 2010
Encrypt R_C using K and the encryption algorithm included in the
SAL.
The method the DSKPP client MUST use to encrypt R_C:
If K is equivalent to K_SERVER (i.e., the public key of the DSKPP
server), then an RSA encryption scheme from PKCS #1 [PKCS-1] MAY
be used. If K is equivalent to K_SERVER, then the cryptographic
module SHOULD verify the server's certificate before using it to
encrypt R_C as described in [RFC2818], Section 3.1, and [RFC5280].
If K is equivalent to K_SHARED, the DSKPP client MAY use the
DSKPP-PRF function to avoid dependence on other algorithms. In
this case, the client uses K_SHARED as input parameter k (K_SHARED
SHOULD be used solely for this purpose) as follows:
dsLen = len(R_C), where "len" is the length of R_C
DS = DSKPP-PRF(K_SHARED, "Encryption" || R_S, dsLen)
This will produce a pseudorandom string DS of length equal to R_C.
Encryption of R_C MAY then be achieved by XOR-ing DS with R_C:
E(DS, R_C) = DS ^ R_C
The DSKPP server will then perform the reverse operation to
extract R_C from E(DS, R_C).
4.2.4. KeyProvClientNonce
DSKPP Client DSKPP Server
------------ ------------
E(K,R_C), AD --->
When this message is sent:
The DSKPP client will send this message immediately following a
<KeyProvServerHello> message whose status was set to "Continue".
Purpose of this message:
With this message the DSKPP client transmits user authentication
data (AD) and a random nonce encrypted with the DSKPP server's key
(K). The client's random nonce is required for each side to agree
upon the same symmetric key (K_TOKEN).
What is contained in this message:
Authentication Data (AD) that was derived from an authentication
code entered by the user before <KeyProvClientHello> was sent
(refer to Section 3.2).
Doherty, et al. Expires March 11, 2011 [Page 31]

Internet-Draft DSKPP September 2010
The DSKPP client's random nonce (R_C), which was encrypted as
described in Section 4.2.3.
How the DSKPP server uses this message:
The DSKPP server MUST use AD to authenticate the user. If
authentication fails, then the DSKPP server MUST set the return
code to a failure status.
If user authentication passes, the DSKPP server decrypts R_C using
its key (K). The decryption method is based on whether K that was
transmitted to the client in <KeyProvServerHello> was equal to the
server's public key (K_SERVER) or a pre-shared key (K_SHARED)
(refer to Section 4.2.3 for a description of how the DSKPP client
encrypts R_C).
After extracting R_C, the DSKPP server computes K_TOKEN using a
combination of the two random nonces R_S and R_C and its
encryption key, K, as described in Section 4.1.2. The particular
realization of DSKPP-PRF (e.g., those defined in Appendix D)
depends on the MAC algorithm contained in the <KeyProvServerHello>
message. The DSKPP server then generates a key package that
contains key usage attributes such as expiry date and length. The
key package MUST NOT include K_TOKEN since in the four-pass
variant K_TOKEN is never transmitted between the DSKPP server and
client. The server stores K_TOKEN and the key package with the
user's account on the cryptographic server.
Finally, the server generates a key confirmation MAC that the
client will use to avoid a false "Commit" message that would cause
the cryptographic module to end up in state in which the server
does not recognize the stored key.
The MAC used for key confirmation MUST be calculated as follows:
msg_hash = SHA-256(msg_1, ..., msg_n)
dsLen = len(msg_hash)
MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || msg_hash, dsLen)
where
MAC The DSKPP Pseudo-Random Function defined in Section 3.4.2 is
used to compute the MAC. The particular realization of DSKPP-
PRF (e.g., those defined in Appendix D) depends on the MAC
algorithm contained in the <KeyProvServerHello> message. The
MAC MUST be computed using the existing MAC key (K_MAC), and a
string that is formed by concatenating the (ASCII) string "MAC
1 computation" and a msg_hash
Doherty, et al. Expires March 11, 2011 [Page 32]

Internet-Draft DSKPP September 2010
K_MAC The key derived from K_PROV, as described in Section 4.1.2.
msg_hash The message hash (defined in Section 3.4.3) of messages
msg_1, ..., msg_n.
4.2.5. KeyProvServerFinished
DSKPP Client DSKPP Server
------------ ------------
<--- KP, MAC
When this message is sent:
The DSKPP server will send this message after authenticating the
user and, if authentication passed, generating K_TOKEN and a key
package, and associating them with the user's account on the
cryptographic server.
Purpose of this message:
With this message the DSKPP server confirms generation of the key
(K_TOKEN), and transmits the associated identifier and
application-specific attributes, but not the key itself, in a key
package to the client for protocol completion.
What is contained in this message:
A status attribute equivalent to the server's return code to
<KeyProvClientNonce>. If user authentication passed, and the
server successfully computed K_TOKEN, generated a key package, and
associated them with the user's account on the cryptographic
server, then it sets Status to Success.
If status is Success, then this message acts as a "commit"
message, instructing the cryptographic module to store the
generated key (K_TOKEN) and associate the given key identifier
with this key. As such, a key package (KP) MUST be included in
this message, which holds an identifier for the generated key (but
not the key itself) and additional configuration, e.g., the
identity of the DSKPP server, key usage attributes, etc. The
default symmetric key package format MUST be based on the Portable
Symmetric Key Container (PSKC) defined in [PSKC]. Alternative
formats MAY include [SKPC-ASN.1], PKCS#12 [PKCS-12], or PKCS#5 XML
[PKCS-5-XML] format.
With KP, the server includes a key confirmation MAC that the
client uses to avoid a false "Commit". The MAC algorithm is the
same DSKPP-PRF that was sent in the <KeyProvServerHello> message.
How the DSKPP client uses this message:
Doherty, et al. Expires March 11, 2011 [Page 33]

Internet-Draft DSKPP September 2010
When the Status attribute is not set to "Success", this indicates
failure and the DSKPP client MUST abort the protocol.
After receiving a <KeyProvServerFinished> message with Status =
"Success", the DSKPP client MUST verify the key confirmation MAC
that was transmitted with this message. The DSKPP client MUST
terminate the DSKPP session if the MAC does not verify, and MUST,
in this case, also delete any nonces, keys, and/or secrets
associated with the failed run of the protocol.
If <KeyProvServerFinished> has Status = "Success" and the MAC was
verified, then the DSKPP client MUST calculate K_TOKEN from the
combination of the two random nonces R_S and R_C and the server's
encryption key, K, as described in Section 4.1.2. The DSKPP-PRF
is the same one used for MAC computation. The DSKPP client
associates the key package contained in <KeyProvServerFinished>
with the generated key, K_TOKEN, and stores this data permanently
on the cryptographic module.
After this operation, it MUST NOT be possible to overwrite the key
unless knowledge of an authorizing key is proven through a MAC on
a later <KeyProvServerHello> (and <KeyProvServerFinished>)
message.
5. Two-Pass Protocol Usage
This section describes the methods and message flow that comprise the
two-pass protocol variant. Two-pass DSKPP is essentially a transport
of keying material from the DSKPP server to the DSKPP client. The
DSKPP server transmits keying material in a key package formatted in
accordance with [PSKC], [SKPC-ASN.1], PKCS#12 [PKCS-12], or PKCS#5
XML [PKCS-5-XML].
The keying material includes a provisioning master key, K_PROV, from
which the DSKPP client derives two keys: the symmetric key to be
established in the cryptographic module, K_TOKEN, and a key, K_MAC,
used for key confirmation. The keying material also includes key
usage attributes, such as expiry date and length.
The DSKPP server encrypts K_PROV to ensure that it is not exposed to
any other entity than the DSKPP server and the cryptographic module
itself. The DSKPP server uses any of three key protection methods to
encrypt K_PROV: Key Transport, Key Wrap, and Passphrase-Based Key
Wrap Key Protection Methods.
While the DSKPP client and server may negotiate the key protection
method to use, the actual key protection is carried out in the
Doherty, et al. Expires March 11, 2011 [Page 34]

Internet-Draft DSKPP September 2010
KeyPackage. The format of a KeyPackage specifies how a key should be
protected using the three key protection methods. The following
KeyPackage formats are defined for DSKPP:
o PSKC Key Container [PSKC] at
urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
o SKPC Key Container [SKPC-ASN.1] at
urn:ietf:params:xml:ns:keyprov:dskpp:skpc-key-container
o PKCS12 Key Container [PKCS-12] at
urn:ietf:params:xml:ns:keyprov:dskpp:pkcs12-key-container
o PKCS5-XML Key Container [PKCS-5-XML] at
urn:ietf:params:xml:ns:keyprov:dskpp:pkcs5-xml-key-container
Each of the key protection methods is described below.
5.1. Key Protection Methods
This section introduces three key protection methods for the two-pass
variant. Additional methods MAY be defined by external entities or
through the IETF process.
5.1.1. Key Transport
Purpose of this method:
This method is intended for PKI-capable devices. The DSKPP server
encrypts keying material and transports it to the DSKPP client.
The server encrypts the keying material using the public key of
the DSKPP client, whose private key part resides in the
cryptographic module. The DSKPP client decrypts the keying
material and uses it to derive the symmetric key, K_TOKEN.
This method is identified with the following URN:
urn:ietf:params:xml:schema:keyprov:dskpp:transport
The DSKPP server and client MUST support the following mechanism:
http://www.w3.org/2001/04/xmlenc#rsa-1_5 encryption mechanism
defined in [XMLENC].
5.1.2. Key Wrap
Purpose of this method:
This method is ideal for pre-keyed devices, e.g., SIM cards. The
DSKPP server encrypts keying material using a pre-shared key
wrapping key and transports it to the DSKPP client. The DSKPP
client decrypts the keying material, and uses it to derive the
Doherty, et al. Expires March 11, 2011 [Page 35]

Internet-Draft DSKPP September 2010
symmetric key, K_TOKEN.
This method is identified with the following URN:
urn:ietf:params:xml:schema:keyprov:dskpp:wrap
The DSKPP server and client MUST support all of the following key
wrapping mechanisms:
AES128 KeyWrap
Refer to id-aes128-wrap in [RFC3394] and
http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
AES128 KeyWrap with Padding
Refer to id-aes128-wrap-pad in [RFC5649] and
http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
AES-CBC-128
Refer to [FIPS197-AES] and
http://www.w3.org/2001/04/xmlenc#aes128-cbc in [XMLENC]
5.1.3. Passphrase-Based Key Wrap
Purpose of this method:
This method is a variation of the Key Wrap Method that is
applicable to constrained devices with keypads, e.g., mobile
phones. The DSKPP server encrypts keying material using a
wrapping key derived from a user-provided passphrase, and
transports the encrypted material to the DSKPP client. The DSKPP
client decrypts the keying material, and uses it to derive the
symmetric key, K_TOKEN.
To preserve the property of not exposing K_TOKEN to any other
entity than the DSKPP server and the cryptographic module itself,
the method SHOULD be employed only when the device contains
facilities (e.g. a keypad) for direct entry of the passphrase.
This method is identified with the following URN:
urn:ietf:params:xml:schema:keyprov:dskpp:passphrase-wrap
The DSKPP server and client MUST support the following:
* The PBES2 password-based encryption scheme defined in [PKCS-5]
(and identified as
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2 in
[PKCS-5-XML])
Doherty, et al. Expires March 11, 2011 [Page 36]

Internet-Draft DSKPP September 2010
When a DSKPP client first connects to a DSKPP server, it is
required to send the <KeyProvClientHello> as its first message.
The client can also send <KeyProvClientHello> in response to a
<KeyProvTrigger> message.
Purpose of this message:
With this message, the DSKPP client specifies its algorithm
preferences and supported key types as well as which DSKPP
versions, protocol variants (in this case "two-pass"), key package
formats, and key protection methods that it supports.
Furthermore, the DSKPP client facilitates user authentication by
transmitting the authentication data (AD) that was provided by the
user before the first DSKPP message was sent.
Application note:
This message MUST send user authentication data (AD) to the DSKPP
server. If this message is preceded by trigger message
<KeyProvTrigger>, then the application will already have AD
available (see Section 4.2.1). However, if this message was not
preceded by <KeyProvTrigger>, then the application MUST retrieve
the user authentication code, possibly by prompting the user to
manually enter their authentication code, e.g., on a device with
only a numeric keypad. The application MUST also derive
Authentication Data (AD) from the authentication code, as
described in Section 3.4.1, and save it for use in its next
message, <KeyProvClientNonce>.
What is contained in this message:
The Security Attribute List (SAL) included with
<KeyProvClientHello> contains the combinations of DSKPP versions,
variants, key package formats, key types, and cryptographic
algorithms that the DSKPP client supports in order of the client's
preference (favorite choice first).
Authentication Data (AD) that was either included with
<KeyProvTrigger>, or generated as described in the "Application
Note" above
The DSKPP client's random nonce (R_C), which was used by the
client when generating AD. By inserting R_C into the DSKPP
session, the DSKPP client is able to ensure the DSKPP server is
live before committing the key.
If <KeyProvClientHello> was preceded by a <KeyProvTrigger>, then
this message MUST also include the DeviceID and/or KeyID that was
provided with the trigger. Otherwise, if a trigger message did
not precede <KeyProvClientHello>, then this message MAY include a
device ID that was pre-shared with the DSKPP server, and MAY
Doherty, et al. Expires March 11, 2011 [Page 38]

Internet-Draft DSKPP September 2010
contain a key ID associated with a key previously provisioned by
the DSKPP provisioning server.
The list of key protection methods (KPML) that the DSKPP client
supports. Each item in the list MAY include an encryption key
"payload" for the DSKPP server to use to protect keying material
that it sends back to the client. The payload MUST be of type
<ds:KeyInfoType> ([XMLDSIG]). For each key protection method, the
allowable choices for <ds:KeyInfoType> are:
* Key Transport
Only those choices of <ds:KeyInfoType> that identify a public
key (i.e., <ds:KeyName>, <ds:KeyValue>, <ds:X509Data>, or <ds:
PGPData>). The <ds:X509Certificate> option of the <ds:
X509Data> alternative is RECOMMENDED when the public key
corresponding to the private key on the cryptographic module
has been certified.
* Key Wrap
Only those choices of <ds:KeyInfoType> that identify a
symmetric key (i.e., <ds:KeyName> and <ds:KeyValue>). The <ds:
KeyName> alternative is RECOMMENDED.
* Passphrase-Based Key Wrap
The <ds:KeyName> option MUST be used and the key name MUST
identify the passphrase that will be used by the server to
generate the key wrapping key. The identifier and passphrase
components of <ds:KeyName> MUST be set to the Client ID and
authentication code components of AD (same AD as contained in
this message).
How the DSKPP server uses this message:
The DSKPP server will look for an acceptable combination of DSKPP
version, variant (in this case, two-pass), key package format, key
type, and cryptographic algorithms. If the DSKPP Client's SAL
does not match the capabilities of the DSKPP Server, or does not
comply with key provisioning policy, then the DSKPP Server will
set the Status attribute to something other than "Success".
Otherwise, Status will be set to "Success".
The DSKPP server will validate the DeviceID and KeyID if included
in <KeyProvClientHello>. The DSKPP server MUST NOT accept the
DeviceID unless the server sent the DeviceID in a preceding
trigger message. Note that it is also legitimate for a DSKPP
client to initiate the DSKPP protocol run without having received
a <KeyProvTrigger> message from a server, but in this case any
provided DeviceID MUST NOT be accepted by the DSKPP server unless
the server has access to a unique key for the identified device
Doherty, et al. Expires March 11, 2011 [Page 39]

Internet-Draft DSKPP September 2010
and that key will be used in the protocol.
The DSKPP server MUST use AD to authenticate the user. If
authentication fails, then the DSKPP server MUST set the return
code to a failure status, and MUST, in this case, also delete any
nonces, keys, and/or secrets associated with the failed run of the
protocol.
If user authentication passes, the DSKPP server generates a key
K_PROV. In the two-pass case, wherein the client does not have
access to R_S, K_PROV is randomly generated solely by the DSKPP
server wherein K_PROV MUST consist of two parts of equal length,
i.e.,
K_PROV = K_MAC || K_TOKEN
The length of K_TOKEN (and hence also the length of K_MAC) is
determined by the type of K_TOKEN, which MUST be one of the key
types supported by the DSKPP client. In cases where the desired
key length for K_TOKEN is different from the length of K_MAC for
the underlying MAC algorithm, the greater length of the two MUST
be chosen to generate K_PROV. The actual MAC key is truncated
from the resulting K_MAC when it is used in the MAC algorithm when
K_MAC is longer than necessary in order to match the desired
K_TOKEN length. If K_TOKEN is longer than needed in order to
match the K_MAC length, the provisioning server and the receiving
client must determine the actual secret key length from the target
key algorithm and store only the truncated portion of the K_TOKEN.
The truncation MUST take the beginning bytes of the desired length
from K_TOKEN or K_MAC for the actual key. For example, when a
provisioning server provisions an event based HOTP secret key with
length 20 and MAC algorithm DSKPP-PRF-SHA256 (Appendix D), K_PROV
length will be 64. The derived K_TOKEN and K_MAC will each
consist of 32 bytes. The actual HOTP key should be the first 20
bytes of the K_TOKEN.
Once K_PROV is computed, the DSKPP server selects one of the key
protection methods from the DSKPP client's KPML, and uses that
method and corresponding payload to encrypt K_PROV. The DSKPP
server generates a key package to transport the key encryption
method information and the encrypted provisioning key (K_PROV).
The encrypted data format is subject to the choice supported by
the selected key package. The key package MUST specify and use
the selected key protection method and the key information that
was received in <KeyProvClientHello>.The key package also includes
key usage attributes such as expiry date and length. The server
stores the key package and K_TOKEN with a user account on the
cryptographic server.
Doherty, et al. Expires March 11, 2011 [Page 40]

Internet-Draft DSKPP September 2010
The server generates a MAC for key confirmation, which the client
will use to avoid a false "Commit" message that would cause the
cryptographic module to end up in state in which the server does
not recognize the stored key.
In addition, if an existing key is being renewed, the server
generates a second MAC that it will return to the client as server
authentication data, AD, so that the DSKPP client can confirm that
the replacement key came from a trusted server.
The method the DSKPP server MUST use to calculate the key
confirmation MAC:
msg_hash = SHA-256(msg_1, ..., msg_n)
dsLen = len(msg_hash)
MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || msg_hash ||
ServerID, dsLen)
where
MAC The MAC MUST be calculated using the already
established MAC algorithm and MUST be computed on the
(ASCII) string "MAC 1 computation", msg_hash, and
ServerID using the existing MAC key K_MAC.
K_MAC The key that is derived from K_PROV which the DSKPP
server MUST provide to the cryptographic module.
msg_hash The message hash, defined in Section 3.4.3, of
messages msg_1, ..., msg_n.
ServerID The identifier that the DSKPP server MUST include in
the <KeyPackage> element of <KeyProvServerFinished>.
If DSKPP-PRF (defined in Section 3.4.2) is used as the MAC
algorithm, then the input parameter s MUST consist of the
concatenation of the (ASCII) string "MAC 1 computation", msg_hash,
and ServerID, and the parameter dsLen MUST be set to the length of
msg_hash.
The method the DSKPP server MUST use to calculate the server
authentication MAC:
The MAC MUST be computed on the (ASCII) string "MAC 2
computation", the server identifier ServerID, and R, using a pre-
existing MAC key K_MAC' (the MAC key that existed before this
protocol run). Note that the implementation may specify K_MAC' to
Doherty, et al. Expires March 11, 2011 [Page 41]

Internet-Draft DSKPP September 2010
be the value of the K_TOKEN that is being replaced.
If DSKPP-PRF is used as the MAC algorithm, then the input
parameter s MUST consist of the concatenation of the (ASCII)
string "MAC 2 computation" ServerID, and R. The parameter dsLen
MUST be set to at least 16 (i.e. the length of the MAC MUST be at
least 16 octets):
dsLen >= 16
MAC = DSKPP-PRF (K_MAC', "MAC 2 computation" || ServerID || R,
dsLen)
The MAC algorithm MUST be the same as the algorithm used by the
DSKPP server to calculate the key confirmation MAC.
5.2.3. KeyProvServerFinished
DSKPP Client DSKPP Server
------------ ------------
<--- KP, MAC, AD
When this message is sent:
The DSKPP server will send this message after authenticating the
user and, if authentication passed, generating K_TOKEN and a key
package, and associating them with the user's account on the
cryptographic server.
Purpose of this message:
With this message the DSKPP server transports a key package
containing the encrypted provisioning key (K_PROV) and key usage
attributes.
What is contained in this message:
A status attribute equivalent to the server's return code to
<KeyProvClientHello>. If the server found an acceptable set of
attributes from the client's SAL, then it sets status to Success.
The confirmation message MUST include the Key Package (KP) that
holds the DSKPP Server's ID, key ID, key type, encrypted
provisioning key (K_PROV), encryption method, and additional
configuration information. The default symmetric key package
format MUST be based on the Portable Symmetric Key Container
(PSKC) defined in [PSKC]. Alternative formats MAY include
[SKPC-ASN.1], PKCS#12 [PKCS-12], or PKCS#5 XML [PKCS-5-XML].
This message MUST include a MAC that the DSKPP client will use for
key confirmation. This key confirmation MAC is calculated using
Doherty, et al. Expires March 11, 2011 [Page 42]

Internet-Draft DSKPP September 2010
the "MAC 1 computation" as described in the previous section.
Finally, if an existing key is being replaced, then this message
MUST also include a server authentication MAC (calculated using
the "MAC 2 computation" as described in the previous section),
which is passed as AD to the DSKPP client.
How the DSKPP client uses this message:
After receiving a <KeyProvServerFinished> message with Status =
"Success", the DSKPP client MUST verify both MACs (MAC and AD).
The DSKPP client MUST terminate the DSKPP protocol run if either
MAC does not verify, and MUST, in this case, also delete any
nonces, keys, and/or secrets associated with the failed run of the
protocol.
If <KeyProvServerFinished> has Status = "Success" and the MACs
were verified, then the DSKPP client MUST extract K_PROV from the
provided key package, and derive K_TOKEN. Finally, the DSKPP
client initializes the cryptographic module with K_TOKEN and the
corresponding key usage attributes. After this operation, it MUST
NOT be possible to overwrite the key unless knowledge of an
authorizing key is proven through a MAC on a later
<KeyProvServerFinished> message.
6. Protocol Extensions
DSKPP has been designed to be extensible. The sub-sections below
define two extensions that are included with the DSKPP schema. Since
it is possible that the use of extensions will harm interoperability,
protocol designers are advised to carefully consider the use of
extensions. For example, if a particular implementation relies on
the presence of a proprietary extension, then it may not be able to
interoperate with independent implementations that have no knowledge
of this extension.
Extensions may be sent with any DSKPP message using the
ExtensionsType. The ExtensionsType type is a list of Extensions
containing type-value pairs that define optional features supported
by a DSKPP client or server. Each extension MAY be marked as
Critical by setting the "Critical" attribute of the Extension to
"true". Unless an extension is marked as Critical, a receiving party
need not be able to interpret it; a receiving party is always free to
disregard any (non-critical) extensions.
Doherty, et al. Expires March 11, 2011 [Page 43]

Internet-Draft DSKPP September 20106.1. The ClientInfoType Extension
The ClientInfoType extension MAY contain any client-specific data
required of an application. This extension MAY be present in a
<KeyProvClientHello> or <KeyProvClientNonce> message. When present,
this extension MUST NOT be marked as Critical.
DSKPP servers MUST support this extension. DSKPP servers MUST NOT
attempt to interpret the data it carries and, if received, MUST
include it unmodified in the current protocol run's next server
response. DSKPP servers need not retain the ClientInfoType data.
6.2. The ServerInfoType Extension
The ServerInfoType extension MAY contain any server-specific data
required of an application, e.g., state information. This extension
is only valid in <KeyProvServerHello> messages for which the Status
attribute is set to "Continue". When present, this extension MUST
NOT be marked as Critical.
DSKPP clients MUST support this extension. DSKPP clients MUST NOT
attempt to interpret the data it carries and, if received, MUST
include it unmodified in the current protocol run's next client
request (i.e., the <KeyProvClientNonce> message). DSKPP clients need
not retain the ServerInfoType data.
7. Protocol Bindings7.1. General Requirements
DSKPP assumes a reliable transport.
7.2. HTTP/1.1 Binding for DSKPP
This section presents a binding of the previous messages to HTTP/1.1
[RFC2616]. This HTTP binding is mandatory-to-implement, although
newer versions of the specification might define additional bindings
in the future. Note that the HTTP client will normally be different
from the DSKPP client (i.e., the HTTP client will "proxy" DSKPP
messages from the DSKPP client to the DSKPP server). Likewise, on
the HTTP server side, the DSKPP server MAY receive DSKPP message from
a "front-end" HTTP server. The DSKPP server will be identified by a
specific URL, which may be pre-configured, or provided to the client
during initialization.
Doherty, et al. Expires March 11, 2011 [Page 44]

Internet-Draft DSKPP September 20107.2.1. Identification of DSKPP Messages
The MIME-type for all DSKPP messages MUST be
application/dskpp+xml
7.2.2. HTTP Headers
In order to avoid caching of responses carrying DSKPP messages by
proxies, the following holds:
o When using HTTP/1.1, requesters SHOULD:
* Include a Cache-Control header field set to "no-cache, no-
store".
* Include a Pragma header field set to "no-cache".
o When using HTTP/1.1, responders SHOULD:
* Include a Cache-Control header field set to "no-cache, no-must-
revalidate, private".
* Include a Pragma header field set to "no-cache".
* NOT include a Validator, such as a Last-Modified or ETag
header.
To handle content negotiation, HTTP requests MAY include an HTTP
Accept header field. This header field SHOULD should be identified
using the MIME type specified in Section 7.2.1. The Accept header
MAY include additional content types defined by future versions of
this protocol.
There are no other restrictions on HTTP headers, besides the
requirement to set the Content-Type header value to the MIME type
specified in Section 7.2.1.
7.2.3. HTTP Operations
Persistent connections as defined in HTTP/1.1 are OPTIONAL. DSKPP
requests are mapped to HTTP requests with the POST method. DSKPP
responses are mapped to HTTP responses.
For the 4-pass DSKPP, messages within the protocol run are bound
together. In particular, <KeyProvServerHello> is bound to the
preceding <KeyProvClientHello> by being transmitted in the
corresponding HTTP response. <KeyProvServerHello> MUST have a
SessionID attribute, and the SessionID attribute of the subsequent
<KeyProvClientNonce> message MUST be identical.
<KeyProvServerFinished> is then once again bound to the rest through
HTTP (and possibly through a SessionID).
Doherty, et al. Expires March 11, 2011 [Page 45]

Internet-Draft DSKPP September 20107.2.4. HTTP Status Codes
A DSKPP HTTP responder that refuses to perform a message exchange
with a DSKPP HTTP requester SHOULD return a 403 (Forbidden) response.
In this case, the content of the HTTP body is not significant. In
the case of an HTTP error while processing a DSKPP request, the HTTP
server MUST return a 500 (Internal Server Error) response. This type
of error SHOULD be returned for HTTP-related errors detected before
control is passed to the DSKPP processor, or when the DSKPP processor
reports an internal error (for example, the DSKPP XML namespace is
incorrect, or the DSKPP schema cannot be located). If a request is
received that is not a DSKPP client message, the DSKPP responder MUST
return a 400 (Bad request) response.
In these cases (i.e., when the HTTP response code is 4xx or 5xx), the
content of the HTTP body is not significant.
Redirection status codes (3xx) apply as usual.
Whenever the HTTP POST is successfully invoked, the DSKPP HTTP
responder MUST use the 200 status code and provide a suitable DSKPP
message (possibly with DSKPP error information included) in the HTTP
body.
7.2.5. HTTP Authentication
No support for HTTP/1.1 authentication is assumed.
7.2.6. Initialization of DSKPP
If a user requests key initialization in a browsing session, and if
that request has an appropriate Accept header (e.g., to a specific
DSKPP server URL), the DSKPP server MAY respond by sending a DSKPP
initialization message in an HTTP response with Content-Type set
according to Section 7.2.1 and response code set to 200 (OK). The
initialization message MAY carry data in its body, such as the URL
for the DSKPP client to use when contacting the DSKPP server. If the
message does carry data, the data MUST be a valid instance of a
<KeyProvTrigger> element.
Note that if the user's request was directed to some other resource,
the DSKPP server MUST NOT respond by combining the DSKPP content type
with response code 200. In that case, the DSKPP server SHOULD
respond by sending a DSKPP initialization message in an HTTP response
with Content-Type set according to Section 7.2.1 and response code
set to 406 (Not Acceptable).
Doherty, et al. Expires March 11, 2011 [Page 46]

Internet-Draft DSKPP September 2010
b. MUST implement the two-pass variation of the protocol (Section 5)
c. MUST support user authentication (Section 3.2.1)
d. MUST support the following key derivation functions:
* DSKPP-PRF-AES DSKPP-PRF realization (Appendix D)
* DSKPP-PRF-SHA256 DSKPP-PRF realization (Appendix D)
e. MUST support the following encryption mechanisms for protection
of the client nonce in the four-pass protocol:
* Mechanism described in Section 4.2.4
f. MUST support one of the following encryption algorithms for
symmetric key operations, e.g., key wrap:
* KW-AES128 without padding; refer to
http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC]
* KW-AES128 with padding; refer to
http://www.w3.org/2001/04/xmlenc#kw-aes128 in [XMLENC] and
[RFC5649]
* AES-CBC-128; refer to [FIPS197-AES]
g. MUST support the following encryption algorithms for asymmetric
key operations, e.g., key transport:
* RSA Encryption Scheme [PKCS-1]
h. MUST support the following integrity/KDF MAC functions:
* DSKPP-PRF-AES (Appendix D)
* DSKPP-PRF-SHA256 (Appendix D)
i. MUST support the PSKC key package [PSKC]; all three PSKC key
protection methods (Key Transport, Key Wrap, and Passphrase-Based
Key Wrap) MUST be implemented
j. MAY support the ASN.1 key package as defined in [SKPC-ASN.1]
DSKPP clients MUST support either the two-pass or the four-pass
variant of the protocol. DSKPP clients MUST fulfill all requirements
listed in item (c) - (j).
Finally, implementations of DSKPP MUST bind DSKPP messages to
HTTP/1.1 as described in Section 7.2.
Of course, DSKPP is a security protocol, and one of its major
functions is to allow only authorized parties to successfully
initialize a cryptographic module with a new symmetric key.
Therefore, a particular implementation may be configured with any of
a number of restrictions concerning algorithms and trusted
authorities that will prevent universal interoperability.
Doherty, et al. Expires March 11, 2011 [Page 57]

Internet-Draft DSKPP September 201010. Security Considerations10.1. General
DSKPP is designed to protect generated keying material from exposure.
No other entities than the DSKPP server and the cryptographic module
will have access to a generated K_TOKEN if the cryptographic
algorithms used are of sufficient strength and, on the DSKPP client
side, generation and encryption of R_C and generation of K_TOKEN take
place as specified in the cryptographic module. This applies even if
malicious software is present in the DSKPP client. However, as
discussed in the following sub-sections, DSKPP does not protect
against certain other threats resulting from man-in-the-middle
attacks and other forms of attacks. DSKPP MUST, therefore, be run
over a transport providing confidentiality and integrity, such as
HTTP over Transport Layer Security (TLS) with a suitable ciphersuite
[RFC2818], when such threats are a concern. Note that TLS
ciphersuites with anonymous key exchanges are not suitable in those
situations [RFC5246].
10.2. Active Attacks10.2.1. Introduction
An active attacker MAY attempt to modify, delete, insert, replay, or
reorder messages for a variety of purposes including service denial
and compromise of generated keying material.
10.2.2. Message Modifications
Modifications to a <KeyProvTrigger> message will either cause denial-
of-service (modifications of any of the identifiers or the
authentication code) or will cause the DSKPP client to contact the
wrong DSKPP server. The latter is in effect a man-in-the-middle
attack and is discussed further in Section 10.2.7.
An attacker may modify a <KeyProvClientHello> message. This means
that the attacker could indicate a different key or device than the
one intended by the DSKPP client, and could also suggest other
cryptographic algorithms than the ones preferred by the DSKPP client,
e.g., cryptographically weaker ones. The attacker could also suggest
earlier versions of the DSKPP protocol, in case these versions have
been shown to have vulnerabilities. These modifications could lead
to an attacker succeeding in initializing or modifying another
cryptographic module than the one intended (i.e., the server
assigning the generated key to the wrong module), or gaining access
to a generated key through the use of weak cryptographic algorithms
or protocol versions. DSKPP implementations MAY protect against the
Doherty, et al. Expires March 11, 2011 [Page 58]

Internet-Draft DSKPP September 2010
latter by having strict policies about what versions and algorithms
they support and accept. The former threat (assignment of a
generated key to the wrong module) is not possible when the shared-
key variant of DSKPP is employed (assuming existing shared keys are
unique per cryptographic module), but is possible in the public-key
variation. Therefore, DSKPP servers MUST NOT accept unilaterally
provided device identifiers in the public-key variation. This is
also indicated in the protocol description. In the shared-key
variation, however, an attacker may be able to provide the wrong
identifier (possibly also leading to the incorrect user being
associated with the generated key) if the attacker has real-time
access to the cryptographic module with the identified key. The
result of this attack could be that the generated key is associated
with the correct cryptographic module but the module is associated
with the incorrect user. See further Section 10.5 for a discussion
of this threat and possible countermeasures.
An attacker may also modify a <KeyProvServerHello> message. This
means that the attacker could indicate different key types,
algorithms, or protocol versions than the legitimate server would,
e.g., cryptographically weaker ones. The attacker may also provide a
different nonce than the one sent by the legitimate server. Clients
MAY protect against the former through strict adherence to policies
regarding permissible algorithms and protocol versions. The latter
(wrong nonce) will not constitute a security problem, as a generated
key will not match the key generated on the legitimate server. Also,
whenever the DSKPP run would result in the replacement of an existing
key, the <Mac> element protects against modifications of R_S.
Modifications of <KeyProvClientNonce> messages are also possible. If
an attacker modifies the SessionID attribute, then, in effect, a
switch to another session will occur at the server, assuming the new
SessionID is valid at that time on the server. It still will not
allow the attacker to learn a generated K_TOKEN since R_C has been
wrapped for the legitimate server. Modifications of the
<EncryptedNonce> element, e.g., replacing it with a value for which
the attacker knows an underlying R'C, will not result in the client
changing its pre-DSKPP state, since the server will be unable to
provide a valid MAC in its final message to the client. The server
MAY, however, end up storing K'TOKEN rather than K_TOKEN. If the
cryptographic module has been associated with a particular user, then
this could constitute a security problem. For a further discussion
about this threat, and a possible countermeasure, see Section 10.5
below. Note that use of TLS does not protect against this attack if
the attacker has access to the DSKPP client (e.g., through malicious
software, "Trojans") [RFC5246].
Finally, attackers may also modify the <KeyProvServerFinished>
Doherty, et al. Expires March 11, 2011 [Page 59]

Internet-Draft DSKPP September 2010
message. Replacing the <Mac> element will only result in denial-of-
service. Replacement of any other element may cause the DSKPP client
to associate, e.g., the wrong service with the generated key. DSKPP
SHOULD be run over a transport providing confidentiality and
integrity when this is a concern.
10.2.3. Message Deletion
Message deletion will not cause any other harm than denial-of-
service, since a cryptographic module MUST NOT change its state
(i.e., "commit" to a generated key) until it receives the final
message from the DSKPP server and successfully has processed that
message, including validation of its MAC. A deleted
<KeyProvServerFinished> message will not cause the server to end up
in an inconsistent state vis-a-vis the cryptographic module if the
server implements the suggestions in Section 10.5.
10.2.4. Message Insertion
An active attacker may initiate a DSKPP run at any time, and suggest
any device identifier. DSKPP server implementations MAY receive some
protection against inadvertently initializing a key or inadvertently
replacing an existing key or assigning a key to a cryptographic
module by initializing the DSKPP run by use of the <KeyProvTrigger>.
The <AuthenticationData> element allows the server to associate a
DSKPP protocol run with, e.g., an earlier user-authenticated session.
The security of this method, therefore, depends on the ability to
protect the <AuthenticationData> element in the DSKPP initialization
message. If an eavesdropper is able to capture this message, he may
race the legitimate user for a key initialization. DSKPP over a
transport providing confidentiality and integrity, coupled with the
recommendations in Section 10.5, is RECOMMENDED when this is a
concern.
Insertion of other messages into an existing protocol run is seen as
equivalent to modification of legitimately sent messages.
10.2.5. Message Replay
During 4-pass DSKPP, attempts to replay a previously recorded DSKPP
message will be detected, as the use of nonces ensures that both
parties are live. For example, a DSKPP client knows that a server it
is communicating with is "live" since the server MUST create a MAC on
information sent by the client.
The same is true for 2-pass DSKPP thanks to the requirement that the
client sends R in the <KeyProvClientHello> message and that the
server includes R in the MAC computation.
Doherty, et al. Expires March 11, 2011 [Page 60]

Internet-Draft DSKPP September 201010.2.6. Message Reordering
An attacker may attempt to re-order 4-pass DSKPP messages but this
will be detected, as each message is of a unique type. Note: Message
re-ordering attacks cannot occur in 2-pass DSKPP since each party
sends at most one message each.
10.2.7. Man-in-the-Middle
In addition to other active attacks, an attacker posing as a man-in-
the-middle may be able to provide his own public key to the DSKPP
client. This threat and countermeasures to it are discussed in
Section 4.1.1. An attacker posing as a man-in-the-middle may also be
acting as a proxy and, hence, may not interfere with DSKPP runs but
still learn valuable information; see Section 10.3.
10.3. Passive Attacks
Passive attackers may eavesdrop on DSKPP runs to learn information
that later on may be used to impersonate users, mount active attacks,
etc.
If DSKPP is not run over a transport providing confidentiality, a
passive attacker may learn:
o What cryptographic modules a particular user is in possession of
o The identifiers of keys on those cryptographic modules and other
attributes pertaining to those keys, e.g., the lifetime of the
keys
o DSKPP versions and cryptographic algorithms supported by a
particular DSKPP client or server
o Any value present in an <extension> that is part of
<KeyProvClientHello>
Whenever the above is a concern, DSKPP MUST be run over a transport
providing confidentiality. If man-in-the-middle attacks for the
purposes described above are a concern, the transport MUST also offer
server-side authentication.
10.4. Cryptographic Attacks
An attacker with unlimited access to an initialized cryptographic
module may use the module as an "oracle" to pre-compute values that
later on may be used to impersonate the DSKPP server. Section 4.1.1
contains a discussion of this threat and steps RECOMMENDED to protect
against it.
Implementers are advised that cryptographic algorithms become weaker
with time. As new cryptographic techniques are developed and
Doherty, et al. Expires March 11, 2011 [Page 61]

Internet-Draft DSKPP September 2010
computing performance improves, the work factor to break a particular
cryptographic algorithm will reduce. Therefore, cryptographic
algorithm implementations SHOULD be modular allowing new algorithms
to be readily inserted. That is, implementers SHOULD be prepared to
regularly update the algorithms in their implementations.
10.5. Attacks on the Interaction between DSKPP and User Authentication
If keys generated in DSKPP will be associated with a particular user
at the DSKPP server (or a server trusted by, and communicating with
the DSKPP server), then in order to protect against threats where an
attacker replaces a client-provided encrypted R_C with his own R'C
(regardless of whether the public-key variation or the shared-secret
variation of DSKPP is employed to encrypt the client nonce), the
server SHOULD NOT commit to associate a generated K_TOKEN with the
given cryptographic module until the user simultaneously has proven
both possession of the device that hosts the cryptographic module
containing K_TOKEN and some out-of-band provided authenticating
information (e.g., an authentication code). For example, if the
cryptographic module is a one-time password token, the user could be
required to authenticate with both a one-time password generated by
the cryptographic module and an out-of-band provided authentication
code in order to have the server "commit" to the generated OTP value
for the given user. Preferably, the user SHOULD perform this
operation from another host than the one used to initialize keys on
the cryptographic module, in order to minimize the risk of malicious
software on the client interfering with the process.
Note: This scenario, wherein the attacker replaces a client-provided
R_C with his own R'C, does not apply to 2-pass DSKPP as the client
does not provide any entropy to K_TOKEN. The attack as such (and its
countermeasures) still applies to 2-pass DSKPP, however, as it
essentially is a man-in-the-middle attack.
Another threat arises when an attacker is able to trick a user to
authenticate to the attacker rather than to the legitimate service
before the DSKPP protocol run. If successful, the attacker will then
be able to impersonate the user towards the legitimate service, and
subsequently receive a valid DSKPP trigger. If the public-key
variant of DSKPP is used, this may result in the attacker being able
to (after a successful DSKPP protocol run) impersonate the user.
Ordinary precautions MUST, therefore, be in place to ensure that
users authenticate only to legitimate services.
10.6. Miscellaneous ConsiderationsDoherty, et al. Expires March 11, 2011 [Page 62]

Internet-Draft DSKPP September 201010.6.1. Client Contributions to K_TOKEN Entropy
In 4-pass DSKPP, both the client and the server provide randomizing
material to K_TOKEN, in a manner that allows both parties to verify
that they did contribute to the resulting key. In the 2-pass DSKPP
version defined herein, only the server contributes to the entropy of
K_TOKEN. This means that a broken or compromised (pseudo-)random
number generator in the server may cause more damage than it would in
the 4-pass variant. Server implementations SHOULD therefore take
extreme care to ensure that this situation does not occur.
10.6.2. Key Confirmation
4-pass DSKPP servers provide key confirmation through the MAC on R_C
in the <KeyProvServerFinished> message. In the 2-pass DSKPP variant
described herein, key confirmation is provided by the MAC including
R, using K_MAC.
10.6.3. Server Authentication
DSKPP servers MUST authenticate themselves whenever a successful
DSKPP 2-pass protocol run would result in an existing K_TOKEN being
replaced by a K_TOKEN', or else a denial-of-service attack where an
unauthorized DSKPP server replaces a K_TOKEN with another key would
be possible. In 2-pass DSKPP, servers authenticate by including the
AuthenticationDataType extension containing a MAC as described in
Section 5 for two-pass DSKPP.
Whenever a successful DSKPP 2-pass protocol run would result in an
existing K_TOKEN being replaced by a K_TOKEN', the DSKPP client and
server MUST do the following to prevent a denial-of-service attack
where an unauthorized DSKPP server replaces a K_TOKEN with another
key:
o The DSKPP server MUST use the AuthenticationDataType extension to
transmit a second MAC, calculated as described in Section 5.2.2.
o The DSKPP client MUST authenticate the server using the MAC
contained in the AuthenticationDataType extension received from
the DSKPP server to which it is connected.
10.6.4. User Authentication
A DSKPP server MUST authenticate a client to ensure that K_TOKEN is
delivered to the intended device. The following measures SHOULD be
considered:
o When an Authentication Code is used for client authentication, a
password dictionary attack on the authentication data is possible.
Doherty, et al. Expires March 11, 2011 [Page 63]

Internet-Draft DSKPP September 2010
o The length of the Authentication Code when used over a non-secure
channel SHOULD be longer than what is used over a secure channel.
When a device, e.g., some mobile phones with small screens, cannot
handle a long Authentication Code in a user-friendly manner, DSKPP
SHOULD rely on a secure channel for communication.
o In the case that a non-secure channel has to be used, the
Authentication Code SHOULD be sent to the server MAC'd as
specified in Section 3.4.1. The Authentication Code and nonce
value MUST be strong enough to prevent offline brute-force
recovery of the Authentication Code from the HMAC data. Given
that the nonce value is sent in plaintext format over a non-secure
transport, the cryptographic strength of the Authentication Data
depends more on the quality of the Authentication Code.
o When the Authentication Code is sent from the DSKPP server to the
device in a DSKPP initialization trigger message, an eavesdropper
may be able to capture this message and race the legitimate user
for a key initialization. To prevent this, the transport layer
used to send the DSKPP trigger MUST provide confidentiality and
integrity, e.g. a secure browser session.
10.6.5. Key Protection in Two-Pass DSKPP
Three key protection methods are defined for the different usages of
2-pass DSKPP, which MUST be supported by a key package format, such
as [PSKC] and [SKPC-ASN.1]. Therefore, key protection in the two-
pass DSKPP is dependent upon the security of the key package format
selected for a protocol run. Some considerations for the Passphrase-
Based Key Wrap method follow.
The passphrase-based key wrap method SHOULD depend upon the PBKDF2
function from [PKCS-5] to generate an encryption key from a
passphrase and salt string. It is important to note that passphrase-
based encryption is generally limited in the security that it
provides despite the use of salt and iteration count in PBKDF2 to
increase the complexity of attack. Implementations SHOULD therefore
take additional measures to strengthen the security of the
passphrase-based key wrap method. The following measures SHOULD be
considered where applicable:
o The passphrase is the same as the one-time password component of
the authentication code (see Section 3.4.1) for a description of
the AC format). The passphrase SHOULD be selected well, and usage
guidelines such as the ones in [NIST-PWD] SHOULD be taken into
account.
o A different passphrase SHOULD be used for every key initialization
wherever possible (the use of a global passphrase for a batch of
cryptographic modules SHOULD be avoided, for example). One way to
achieve this is to use randomly-generated passphrases.
Doherty, et al. Expires March 11, 2011 [Page 64]

Internet-Draft DSKPP September 2010
o The passphrase SHOULD be protected well if stored on the server
and/or on the cryptographic module and SHOULD be delivered to the
device's user using secure methods.
o User pre-authentication SHOULD be implemented to ensure that
K_TOKEN is not delivered to a rogue recipient.
o The iteration count in PBKDF2 SHOULD be high to impose more work
for an attacker using brute-force methods (see [PKCS-5] for
recommendations). However, it MUST be noted that the higher the
count, the more work is required on the legitimate cryptographic
module to decrypt the newly delivered K_TOKEN. Servers MAY use
relatively low iteration counts to accommodate devices with
limited processing power such as some PDA and cell phones when
other security measures are implemented and the security of the
passphrase-based key wrap method is not weakened.
o Transport level security [RFC5246] SHOULD be used where possible
to protect a two-pass protocol run. Transport level security
provides a second layer of protection for the newly generated
K_TOKEN.
10.6.6. Algorithm Agility
Many protocols need to be algorithm agile. One reason for this is
that in the past many protocols had fixed sized fields for
information such as hash outputs, keys, etc. This is not the case
for DSKPP, except for the key size in the computation of DSKPP-PRF.
Another reason was that protocols did not support algorithm
negotiation. This is also not the case for DSKPP, except for the use
of SHA-256 in the MAC confirmation message. Updating the key size
for DSKPP-PRF or the MAC confirmation message algorithm will require
a new version of the protocol, which is supported with the Version
attribute.
11. Internationalization Considerations
The DSKPP protocol is meant for machine-to-machine communications; as
such, its elements are tokens not meant for direct human consumption.
DSKPP exchanges information using XML. All XML processors are
required to understand UTF-8 [RFC3629] encoding, and therefore all
DSKPP clients and servers MUST understand UTF-8 encoded XML.
Additionally, DSKPP servers and clients MUST NOT encode XML with
encodings other than UTF-8.
12. IANA Considerations
This document requires several IANA registrations, detailed below.
Doherty, et al. Expires March 11, 2011 [Page 65]

Internet-Draft DSKPP September 2010
To: ietf-types@iana.org
Subject: Registration of MIME media type application/dskpp+xml
MIME media type name: application
MIME subtype name: dskpp+xml
Required parameters: (none)
Optional parameters: charset
Indicates the character encoding of enclosed XML.
Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See
[RFC3203], Section 3.2. Implementations need to support UTF-8
[RFC3629].
Security considerations: This content type is designed to carry
protocol data related to key management. Security mechanisms are
built into the protocol to ensure that various threats are dealt
with. Refer to Section 10 of the Published Specification for more
details
Interoperability considerations: None
Published specification: RFC XXXX [NOTE TO IANA/RFC-EDITOR: Please
replace XXXX with the RFC number for this specification.]
Applications which use this media type: Protocol for key exchange.
Additional information:
Magic Number(s): (none)
File extension(s): .xmls
Macintosh File Type Code(s): (none)
Person & email address to contact for further information:
Andrea Doherty (andrea.doherty@rsa.com)
Intended usage: LIMITED USE
Author/Change controller: The IETF
Other information: This media type is a specialization of
application/xml [RFC3203], and many of the considerations
described there also apply to application/dskpp+xml.
12.4. Status Code Registration
This section registers status codes included in each DSKPP response
message. The status codes are defined in the schema in the
<StatusCode> type definition contained in the XML schema in
Section 8. The following summarizes the registry:
Related Registry:
KEYPROV DSKPP Registries, Status codes for DSKPP
Defining RFC:
RFC XXXX [NOTE TO IANA/RFC-EDITOR: Please replace XXXX with the
RFC number for this specification.]
Doherty, et al. Expires March 11, 2011 [Page 67]

Internet-Draft DSKPP September 2010
Registration/Assignment Procedures:
Following the policies outlined in [RFC3575], the IANA policy for
assigning new values for the status codes for DSKPP MUST be
"Specification Required" and their meanings MUST be documented in
an RFC or in some other permanent and readily available reference,
in sufficient detail that interoperability between independent
implementations is possible. No mechanism to mark entries as
"deprecated" is envisioned. It is possible to update entries from
the registry.
Registrant Contact:
IETF, KEYPROV working group (keyprov@ietf.org),
Andrea Doherty (andrea.doherty@rsa.com)
12.5. DSKPP Version Registration
This section registers DSKPP version numbers. The registry has the
following structure:
+-------------------------------------------+
| DSKPP Version | Specification |
+-------------------------------------------+
| 1.0 | [This document] |
+-------------------------------------------+
Standards action is required to define new versions of DSKPP. It is
not envisioned to deprecate, delete, or modify existing DSKPP
versions.
12.6. PRF Algorithm ID Sub-Registry
This specification relies on a cryptographic primitive, called
"DSKPP-PRF" that provides a deterministic transformation of a secret
key k and a varying length octet string s to a bit string of
specified length dsLen. From the point of view of this
specification, DSKPP-PRF is a "black-box" function that, given the
inputs, generates a pseudorandom value that can be realized by any
appropriate and competent cryptographic technique. . Section 3.4.2
provides two realizations of DSKPP-PRF, DSKPP-PRF-AES and DSKPP-PRF-
SHA256.
This section registers the identifiers associated with these
realizations. PRF Algorithm ID Sub-registries are to be subject to
Specification Required as per RFC 5226 [RFC5226]. Updates MUST be
documented in an RFC or in some other permanent and readily available
reference, in sufficient detail that interoperability between
independent implementations is possible.
Expert approval is required to deprecate a sub-registry. Once
Doherty, et al. Expires March 11, 2011 [Page 68]

Internet-Draft DSKPP September 2010
deprecated, the PRF Algorithm ID SHOULD NOT be used in any new
implementations.
12.6.1. DSKPP-PRF-AES
Common Name:
DSKPP-PRF-AES
URI:
urn:ietf:params:xml:ns:keyprov:dskpp:prf-aes-128
Identifier Definition:
The DSKPP-PRF-AES algorithm realization is defined in
Appendix D.2.2 of this document.
Registrant Contact:
IETF, KEYPROV working group (keyprov@ietf.org),
Andrea Doherty (andrea.doherty@rsa.com)
12.6.2. DSKPP-PRF-SHA256
Common Name:
DSKPP-PRF-SHA256
URI:
urn:ietf:params:xml:ns:keyprov:dskpp:prf-sha256
Identifier Definition:
The DSKPP-PRF-SHA256 algorithm realization is defined in
Appendix D.3.2 of this document.
Registrant Contact:
IETF, KEYPROV working group (keyprov@ietf.org),
Andrea Doherty (andrea.doherty@rsa.com)
12.7. Key Container Registration
This section registers the Key Container type.
Key Container:
The registration name for the Key Container.
Specification:
Key Container defines a key package format that specifies how a
key should be protected using the three key protection methods
provided in Section 5.1.
Doherty, et al. Expires March 11, 2011 [Page 69]

Internet-Draft DSKPP September 2010
Registration Procedure:
Following the policies outlined in [RFC3575], the IANA policy for
assigning new values for the status codes for DSKPP MUST be
"Specification Required" and their meanings MUST be documented in
an RFC or in some other permanent and readily available reference,
in sufficient detail that interoperability between independent
implementations is possible.
Deprecated:
TRUE if based on expert approval this entry has been deprecated
and SHOULD NOT be used in any new implementations. Otherwise
FALSE.
Identifiers:
The initial URIs for the Key Container defined for this version of
the document are listed here:
Name: PSKC Key Container
URI: urn:ietf:params:xml:ns:keyprov:dskpp:pskc-key-container
Specification: [PSKC]
Deprecated: FALSE
Name: SKPC Key Container
URI: urn:ietf:params:xml:ns:keyprov:dskpp:skpc-key-container
Specification: [SKPC-ASN.1]
Deprecated: FALSE
Name: PKCS12 Key Container
URI: urn:ietf:params:xml:ns:keyprov:dskpp:pkcs12-key-container
Specification: [PKCS-12]
Deprecated: FALSE
Name: PKCS5-XML Key Container
URI: urn:ietf:params:xml:ns:keyprov:dskpp:pkcs5-xml-key-container
Specification: [PKCS-5-XML]
Deprecated: FALSE
Registrant Contact:
IETF, KEYPROV working group (keyprov@ietf.org),
Andrea Doherty (andrea.doherty@rsa.com)
13. Intellectual Property Considerations
RSA and RSA Security are registered trademarks or trademarks of RSA
Security Inc. in the United States and/or other countries. The names
of other products and services mentioned may be the trademarks of
their respective owners.
Doherty, et al. Expires March 11, 2011 [Page 70]

Internet-Draft DSKPP September 201014. Contributors
This work is based on information contained in [RFC4758], authored by
Magnus Nystrom, with enhancements borrowed from an individual
Internet-Draft co-authored by Mingliang Pei and Salah Machani (e.g.,
User Authentication, and support for multiple key package formats).
We would like to thank Philip Hoyer for his work in aligning DSKPP
and PSKC schemas.
We would also like to thank Hannes Tschofenig and Phillip Hallam-
Baker for their draft reviews, feedback, and text contributions.
15. Acknowledgements
We would like to thank the following for review of previous DSKPP
document versions:
o Dr. Ulrike Meyer (Review June 2007)
o Niklas Neumann (Review June 2007)
o Shuh Chang (Review June 2007)
o Hannes Tschofenig (Review June 2007 and again in August 2007)
o Sean Turner (Reviews August 2007 and again in July 2008)
o John Linn (Review August 2007)
o Philip Hoyer (Review September 2007)
o Thomas Roessler (Review November 2007)
o Lakshminath Dondeti (Comments December 2007)
o Pasi Eronen (Comments December 2007)
o Phillip Hallam-Baker (Review and Edits November 2008 and again in
January 2009)
o Alexey Melnikov (Review May 2010)
o Peter Saint-Andre (Review May 2010)
We would also like to thank the following for their input to selected
design aspects of the DSKPP protocol:
o Anders Rundgren (Key Package Format and Client Authentication
Data)
o Thomas Roessler (HTTP Binding)
o Hannes Tschofenig (HTTP Binding)
o Phillip Hallam-Baker (Registry for Algorithms)
o N. Asokan (original observation of weakness in Authentication
Data)
Finally, we would like to thank Robert Griffin for opening
communication channels for us with the IEEE P1619.3 Key Management
Group, and facilitating our groups in staying informed of potential
Doherty, et al. Expires March 11, 2011 [Page 71]

Internet-Draft DSKPP September 2010A.2. Multiple Key Requests
A cryptographic module makes multiple requests for symmetric keys
from the same provisioning server. The symmetric keys need not be of
the same type, i.e., the keys may be used with different symmetric
key cryptographic algorithms, including one-time password
authentication algorithms, and the AES encryption algorithm.
A.3. User Authentication
In some deployment scenarios, a key issuer may rely on a third party
provisioning service. In this case, the issuer directs provisioning
requests from the cryptographic module to the provisioning service.
As such, it is the responsibility of the issuer to authenticate the
user through some out-of-band means before granting him rights to
acquire keys. Once the issuer has granted those rights, the issuer
provides an authentication code to the user and makes it available to
the provisioning service, so that the user can prove that he is
authorized to acquire keys.
A.4. Provisioning Time-Out Policy
An issuer may provide a time-limited authentication code to a user
during registration, which the user will input into the cryptographic
module to authenticate themselves with the provisioning server. The
server will allow a key to be provisioned to the cryptographic module
hosted by the user's device when user authentication is required only
if the user inputs a valid authentication code within the fixed time
period established by the issuer.
A.5. Key Renewal
A cryptographic module requests renewal of the symmetric key material
attached to a key ID, as opposed to keeping the key value constant
and refreshing the metadata. Such a need may occur in the case when
a user wants to upgrade her device that houses the cryptographic
module or when a key has expired. When a user uses the same
cryptographic module to, for example, perform strong authentication
at multiple Web login sites, keeping the same key ID removes the need
for the user to register a new key ID at each site.
A.6. Pre-Loaded Key Replacement
This scenario represents a special case of symmetric key renewal in
which a local administrator can authenticate the user procedurally
before initiating the provisioning process. It also allows for a
device issuer to pre-load a key onto a cryptographic module with a
restriction that the key is replaced with a new key prior to use of
Doherty, et al. Expires March 11, 2011 [Page 76]

Internet-Draft DSKPP September 2010
the cryptographic module. Another variation of this scenario is the
organization who recycles devices. In this case, a key issuer would
provision a new symmetric key to a cryptographic module hosted on a
device that was previously owned by another user.
Note that this usage scenario is essentially the same as the previous
scenario wherein the same key ID is used for renewal.
A.7. Pre-Shared Manufacturing Key
A cryptographic module is loaded onto a smart card after the card is
issued to a user. The symmetric key for the cryptographic module
will then be provisioned using a secure channel mechanism present in
many smart card platforms. This allows a direct secure channel to be
established between the smart card chip and the provisioning server.
For example, the card commands (i.e., Application Protocol Data
Units, or APDUs) are encrypted with a pre-issued card manufacturer's
key and sent directly to the smart card chip, allowing secure post-
issuance in-the-field provisioning. This secure flow can pass
Transport Layer Security (TLS) [RFC5246] and other transport security
boundaries.
Note that two pre-conditions for this usage scenario are for the
protocol to be tunneled and the provisioning server to know the
correct pre-established manufacturer's key.
A.8. End-to-End Protection of Key Material
In this scenario, transport layer security does not provide end-to-
end protection of keying material transported from the provisioning
server to the cryptographic module. For example, TLS may terminate
at an application hosted on a PC rather than at the cryptographic
module (i.e., the endpoint) located on a data storage device
[RFC5246]. Mutually authenticated key agreement provides end-to-end
protection, which TLS cannot provide.
Appendix B. Examples
This appendix contains example messages that illustrate parameters,
encoding, and semantics in four-and two- pass DSKPP exchanges. The
examples are written using XML, and are syntactically correct. MAC
and cipher values are fictitious however. This appendix forms an
informative part of the document.
Doherty, et al. Expires March 11, 2011 [Page 77]

Internet-Draft DSKPP September 2010C.1. The 4-pass Variant
When performing 4-pass DSKPP with a cryptographic module using the
PKCS #11 programming interface, the procedure described in
[CT-KIP-P11], Appendix B, is RECOMMENDED.
C.2. The 2-pass Variant
A suggested procedure to perform 2-pass DSKPP with a cryptographic
module through the PKCS #11 interface using the mechanisms defined in
[CT-KIP-P11] is as follows:
a. On the client side,
1. The client selects a suitable slot and token (e.g., through
use of the <DeviceIdentifier> or the <PlatformInfo> element
of the DSKPP trigger message).
2. A nonce R is generated, e.g. by calling C_SeedRandom and
C_GenerateRandom.
3. The client sends its first message to the server, including
the nonce R.
b. On the server side,
1. A generic key K_PROV = K_TOKEN | K_MAC (where '|' denotes
concatenation) is generated, e.g. by calling C_GenerateKey
(using key type CKK_GENERIC_SECRET). The template for K_PROV
MUST allow it to be exported (but only in wrapped form, i.e.
CKA_SENSITIVE MUST be set to CK_TRUE and CKA_EXTRACTABLE MUST
also be set to CK_TRUE), and also to be used for further key
derivation. From K, a token key K_TOKEN of suitable type is
derived by calling C_DeriveKey using the PKCS #11 mechanism
CKM_EXTRACT_KEY_FROM_KEY and setting the CK_EXTRACT_PARAMS to
the first bit of the generic secret key (i.e. set to 0).
Likewise, a MAC key K_MAC is derived from K_PROV by calling
C_DeriveKey using the CKM_EXTRACT_KEY_FROM_KEY mechanism,
this time setting CK_EXTRACT_PARAMS to the length of K_PROV
(in bits) divided by two.
2. The server wraps K_PROV with either the public key of the
DSKPP client or device, the pre-shared secret key, or the
derived shared secret key by using C_WrapKey. If use of the
DSKPP key wrap algorithm has been negotiated then the
CKM_KIP_WRAP mechanism MUST be used to wrap K. When calling
C_WrapKey, the hKey handle in the CK_KIP_PARAMS structure
MUST be set to NULL_PTR. The pSeed parameter in the
CK_KIP_PARAMS structure MUST point to the nonce R provided by
the DSKPP client, and the ulSeedLen parameter MUST indicate
the length of R. The hWrappingKey parameter in the call to
C_WrapKey MUST be set to refer to the key wrapping key.
Doherty, et al. Expires March 11, 2011 [Page 96]

Internet-Draft DSKPP September 2010
3. Next, the server needs to calculate a MAC using K_MAC. If
use of the DSKPP MAC algorithm has been negotiated, then the
MAC is calculated by calling C_SignInit with the CKM_KIP_MAC
mechanism followed by a call to C_Sign. In the call to
C_SignInit, K_MAC MUST be the signature key, the hKey
parameter in the CK_KIP_PARAMS structure MUST be set to
NULL_PTR, the pSeed parameter of the CT_KIP_PARAMS structure
MUST be set to NULL_PTR, and the ulSeedLen parameter MUST be
set to zero. In the call to C_Sign, the pData parameter MUST
be set to the concatenation of the string ServerID and the
nonce R, and the ulDataLen parameter MUST be set to the
length of the concatenated string. The desired length of the
MAC MUST be specified through the pulSignatureLen parameter
and MUST be set to the length of R.
4. If the server also needs to authenticate its message (due to
an existing K_TOKEN being replaced), the server MUST
calculate a second MAC. Again, if use of the DSKPP MAC
algorithm has been negotiated, then the MAC is calculated by
calling C_SignInit with the CKM_KIP_MAC mechanism followed by
a call to C_Sign. In this call to C_SignInit, the K_MAC'
existing before this DSKPP protocol run MUST be the signature
key (the implementation may specify K_MAC' to be the value of
the K_TOKEN that is being replaced, or a version of K_MAC
from the previous protocol run), the hKey parameter in the
CK_KIP_PARAMS structure MUST be set to NULL, the pSeed
parameter of the CT_KIP_PARAMS structure MUST be set to
NULL_PTR, and the ulSeedLen parameter MUST be set to zero.
In the call to C_Sign, the pData parameter MUST be set to the
concatenation of the string ServerID and the nonce R, and the
ulDataLen parameter MUST be set to the length of concatenated
string. The desired length of the MAC MUST be specified
through the pulSignatureLen parameter and MUST be set to the
length of R.
5. The server sends its message to the client, including the
wrapped key K_TOKEN, the MAC and possibly also the
authenticating MAC.
c. On the client side,
1. The client calls C_UnwrapKey to receive a handle to K. After
this, the client calls C_DeriveKey twice: Once to derive
K_TOKEN and once to derive K_MAC. The client MUST use the
same mechanism (CKM_EXTRACT_KEY_FROM_KEY) and the same
mechanism parameters as used by the server above. When
calling C_UnwrapKey and C_DeriveKey, the pTemplate parameter
MUST be used to set additional key attributes in accordance
with local policy and as negotiated and expressed in the
protocol. In particular, the value of the <KeyID> element in
the server's response message MAY be used as CKA_ID for
K_TOKEN. The key K_PROV MUST be destroyed after deriving
Doherty, et al. Expires March 11, 2011 [Page 97]

Internet-Draft DSKPP September 2010
K_TOKEN and K_MAC.
2. The MAC is verified in a reciprocal fashion as it was
generated by the server. If use of the CKM_KIP_MAC mechanism
has been negotiated, then in the call to C_VerifyInit, the
hKey parameter in the CK_KIP_PARAMS structure MUST be set to
NULL_PTR, the pSeed parameter MUST be set to NULL_PTR, and
ulSeedLen MUST be set to 0. The hKey parameter of
C_VerifyInit MUST refer to K_MAC. In the call to C_Verify,
pData MUST be set to the concatenation of the string ServerID
and the nonce R, and the ulDataLen parameter MUST be set to
the length of the concatenated string, pSignature to the MAC
value received from the server, and ulSignatureLen to the
length of the MAC. If the MAC does not verify the protocol
session ends with a failure. The token MUST be constructed
to not "commit" to the new K_TOKEN or the new K_MAC unless
the MAC verifies.
3. If an authenticating MAC was received (REQUIRED if the new
K_TOKEN will replace an existing key on the token), then it
is verified in a similar vein but using the K_MAC' associated
with this server and existing before the protocol run (the
implementation may specify K_MAC' to be the value of the
K_TOKEN that is being replaced, or a version of K_MAC from
the previous protocol run). Again, if the MAC does not
verify the protocol session ends with a failure, and the
token MUST be constructed no to "commit" to the new K_TOKEN
or the new K_MAC unless the MAC verifies.
Appendix D. Example of DSKPP-PRF RealizationsD.1. Introduction
This example appendix defines DSKPP-PRF in terms of AES [FIPS197-AES]
and HMAC [RFC2104]. This appendix forms a normative part of the
document.
D.2. DSKPP-PRF-AESD.2.1. Identification
For cryptographic modules supporting this realization of DSKPP-PRF,
the following URN MUST be used to identify this algorithm in DSKPP:
urn:ietf:params:xml:ns:keyprov:dskpp:prf-aes-128
When this URN is used to identify the encryption algorithm, the
method for encryption of R_C values described in Section 4.2.4 MUST
be used.
Doherty, et al. Expires March 11, 2011 [Page 98]